fix(console): stop truncating task fields column

[hawkw]

Currently, there's a bug where the console's task list view truncates
the fields column to the first ten characters, even when there are
characters remaining in the window to display more of the fields column.
This is due to tui's layout constraints system apparently choosing to
give that column only the minimum number of characters specified,
instead of giving it all the remaining characters not used by other
columns.

I couldn't figure out how to get tui to actually do what we want
(there doesn't seem to be a Constrait for saying "use any remaining
characters not needed for satisfying previous layout constraints"), so I
just kind of hacked around it by adding up all the other columns,
subtracting their widths from the total width of the window, and
specifying that as a "minimum" constraint.

This is kinda ugly, but it seems to work.

Before:

After:

Signed-off-by: Eliza Weisman eliza@buoyant.io

[hawkw]

Apparently there is some known weird behavior with tui's constraint system: fdehau/tui-rs#499