Add a custom mouse event wrapper around tcell's one

[n-peugnet]

This wrapper implements the HasMotion() function which value is set by the main application based on the previous mouse event.

If I understood gdamore/tcell#622 (comment) correctly (emphasis is mine):

Just so we are clear here -- what discriminates a "click" vs. a held drag, is that a click will send an event with buttons set to none. If you get multiple location reports with the buttons unchanged, then the user has been holding the buttons.

With this change, we should be able to use upstream tcell. See #10

I tested this quickly in Gomuks and the selection of text in the message input seemd to behave as expected.

[nileshpatra]

Shouldn't go.mod also be updated to point to gdamore/tcell?

[n-peugnet]

Shouldn't go.mod also be updated to point to gdamore/tcell?

This can be done afterwards, but I can also add it in this pull request. I already have it ready in n-peugnet@5017f77 (then I am able to build Gomuks with this commit n-peugnet/gomuks@ad0c752).
What do you think @tulir?

[nileshpatra]

@tulir can you please review/merge this? This would be very very useful for maintaining gomuks in Debian

[nileshpatra]

Shouldn't go.mod also be updated to point to gdamore/tcell?

This can be done afterwards, but I can also add it in this pull request. I already have it ready in n-peugnet@5017f77 (then I am able to build Gomuks with this commit n-peugnet/gomuks@ad0c752). What do you think @tulir?

Now that this PR is merged, can the change to point it to gdamore/tcell go in?

[n-peugnet]

Now that this PR is merged, can the change to point it to gdamore/tcell go in?

I just made a new pull request for this: #12

[nileshpatra]

I built gomuks with your commits. It does build, however unfortunately, the scrolls do not work properly for me. I try to scroll up/down and nothing happens, or it goes up/down after several attempts. That isn't the case for gomuks built w/o these commits.

Asked @alexmyczko to check as well.

[n-peugnet]

the scrolls do not work properly for me. I try to scroll up/down and nothing happens, or it goes up/down after several attempts.

Sorry, you are right, I didn't test this enough. Simply checking that the buttons bitset is the same is not enough.