Resolve mypy issues in 'qml_utils.py'

Get rid of

uwsift/control/qml_utils.py:87: error: Name "layerModel" already defined on line 83  [no-redef]
uwsift/control/qml_utils.py:96: error: Name "convFuncModel" already defined on line 92  [no-redef]
uwsift/control/qml_utils.py:132: error: Name "layerToDisplay" already defined on line 127  [no-redef]
uwsift/control/qml_utils.py:144: error: Name "dateToDisplay" already defined on line 137  [no-redef]
uwsift/control/qml_utils.py:221: error: Property "timestamps" defined in "TimebaseModel" is read-only  [misc]
uwsift/control/qml_utils.py:222: error: Cannot assign to a method  [assignment]
uwsift/control/qml_utils.py:222: error: Incompatible types in assignment (expression has type "None", variable has type "Callable[..., Any]")  [assignment]
uwsift/control/qml_utils.py:243: error: Name "currentTimestamp" already defined on line 239  [no-redef]
uwsift/control/qml_utils.py:261: error: Name "timestamps" already defined on line 248  [no-redef]
uwsift/control/qml_utils.py:261: error: "Callable[[TimebaseModel], Any]" has no attribute "setter"  [attr-defined]

by
- ignoring false positives for pyqtProperty setters, see
  python/mypy#9911
- Avoiding to initialize variable with None which can also be
  initialized with something more useful right away.

uwsift/control/qml_utils.py

@@ -84,7 +84,7 @@ def set_convenience_functions(self, conv_funcs):
     def layerModel(self):
         return self._qml_layer_model
 
-    @layerModel.setter
+    @layerModel.setter  # type: ignore # mypy bug #9911
     def layerModel(self, new_model):
         self._qml_layer_model = new_model
         self.layerModelChanged.emit()
@@ -93,7 +93,7 @@ def layerModel(self, new_model):
     def convFuncModel(self):
         return self._conv_func_model
 
-    @convFuncModel.setter
+    @convFuncModel.setter  # type: ignore # mypy bug #9911
     def convFuncModel(self, new_model):
         self._conv_func_model = new_model
         self.convFuncModelChanged.emit()
@@ -129,7 +129,7 @@ def layerToDisplay(self):
         return self._layer_to_display
 
     # Define the setter of the 'name' property.
-    @layerToDisplay.setter
+    @layerToDisplay.setter  # type: ignore # mypy bug #9911
     def layerToDisplay(self, data_layer_str):
         self._layer_to_display = data_layer_str
         self.layerToDisplayChanged.emit()
@@ -141,7 +141,7 @@ def dateToDisplay(self):
         else:
             return self._date_to_display
 
-    @dateToDisplay.setter
+    @dateToDisplay.setter  # type: ignore # mypy bug #9911
     def dateToDisplay(self, new_date):
         self._date_to_display = new_date.strftime(self._format_str)
         self.dateToDisplayChanged.emit(self._date_to_display)
@@ -219,7 +219,8 @@ def __init__(self, *args, timestamps: List[QDateTime], **kwargs):
         super().__init__(*args, **kwargs)
         self._format_str = DEFAULT_TIME_FORMAT
         self.timestamps = timestamps  # sets self._timestamps
-        self.currentTimestamp = None  # sets self._current_timestamp
+
+        self._current_timestamp = self._format_str.replace("%", "")
 
     @pyqtProperty("QVariantList", notify=modelChanged)
     def model(self):
@@ -240,7 +241,7 @@ def at(self, i):
     def currentTimestamp(self):
         return self._current_timestamp
 
-    @currentTimestamp.setter
+    @currentTimestamp.setter  # type: ignore # mypy bug #9911
     def currentTimestamp(self, new_date):
         self._current_timestamp = new_date.strftime(self._format_str) if new_date else self._format_str.replace("%", "")
         self.currentTimestampChanged.emit(self._current_timestamp)
@@ -249,15 +250,6 @@ def currentTimestamp(self, new_date):
     def timestamps(self):
         return self._timestamps
 
-    def clear(self):
-        """Set the two corresponding properties which has to do something with the timestamps to None.
-
-        The purpose of this is to give a possibility to return to a similar state like
-        when TimeBaseModel was initialized."""
-        self.timestamps = None
-        self.currentTimestamp = None
-        self.returnToInitialState.emit()
-
     @timestamps.setter
     def timestamps(self, timestamps):
         self.layoutAboutToBeChanged.emit()
@@ -271,6 +263,15 @@ def timestamps(self, timestamps):
         self.layoutChanged.emit()
         self.timebaseChanged.emit()
 
+    def clear(self):
+        """Set the two corresponding properties which has to do something with the timestamps to None.
+
+        The purpose of this is to give a possibility to return to a similar state like
+        when TimeBaseModel was initialized."""
+        self.timestamps = None
+        self.currentTimestamp = None
+        self.returnToInitialState.emit()
+
     @staticmethod
     def _get_default_qdts(steps=5):
         """Generate default QDateTime steps.