Update unit scroller behavior when no moves left & fix alert button getting focus

[DanVanAtta]

commit 95649dc

Update unit scroller behavior when no moves left

1) When no moves left:
- do not render the territory label
- if skipping the last unit, getting to zero moves
  left, then remove the unit avatar rendering image

2) Also, (cleanup) remove an unnecessary update to
   'movesLeft' in territory listener. Changing territory
   hover should not change the moves left and is not a
   necessary invocation.

commit 7910ed8

Remove focusable from 'alert' button

Clicking the alert button repeatedly has no real effect, a user
typically does not want to do this. After a first click, the button
gains focus. *Then* pressing space will activate the button. This
is confusing behavior as the next available unit is selected
and it seems like we are 'skipping' units with the space button
but we are really pressing 'wake-all' repeatedly.

To avoid this confusing scenario, remove focusable from 'alert'
button. This way if it is clicked, and then a user presses space,
that will activate the 'skip' button.

Functional Changes

[] New map or map update
[] New Feature
[x] Feature update or enhancement
[] Feature Removal
[] Code Cleanup or refactor
[] Configuration Change
[] Problem fix:
[] Other:

Testing

• some play testing

[codeclimate]

Code Climate has analyzed commit 7910ed8 and detected 0 issues on this pull request.

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[codecov]

Codecov Report

Merging #6153 into master will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #6153      +/-   ##
============================================
- Coverage     22.95%   22.94%   -0.02%     
- Complexity     6598     6599       +1     
============================================
  Files          1104     1104              
  Lines         78344    78375      +31     
  Branches      11412    11415       +3     
============================================
- Hits          17983    17980       -3     
- Misses        58166    58197      +31     
- Partials       2195     2198       +3     

Impacted Files	Coverage Δ	Complexity Δ
...trategy/triplea/ui/unit/scroller/UnitScroller.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...ine/message/unifiedmessenger/UnifiedMessenger.java	67.68% <0.00%> (-7.49%)	27.00% <0.00%> (+2.00%)	⬇️
...ames/strategy/engine/message/RemoteMethodCall.java	85.07% <0.00%> (-5.41%)	32.00% <0.00%> (+1.00%)	⬇️
.../triplea/delegate/battle/UnitBattleComparator.java	31.09% <0.00%> (-1.69%)	14.00% <0.00%> (-2.00%)

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[RoiEXLab]

I was so confused. I was asking myself, what are movesLeft supposed to be and why aren't there any movesRight?
We'll after realizing my mistake I suggest renaming the fields and methods to movesRemaining or something 😅

[DanVanAtta]

😄 Nothing really coming to mind for a better name without getting super wordy. movesRemaining invites a problem where it seems like a list of moves rather than a count. So we then get to movesRemainingCount, which then leads to how do we rename the "updateMovesLeft()" method as well.