MissionStatus Enum

[Windchild292]

This PR swaps MissionStatus from magic numbers to an enum.

As part of this I reworked the CompleteMissionDialog, which is the first commit.

[NickAragua]

One suggestion, looks fine otherwise.

[codecov]

Codecov Report

Merging #2151 (98253ba) into master (559cb00) will increase coverage by 0.01%.
The diff coverage is 19.14%.

@@             Coverage Diff              @@
##             master    #2151      +/-   ##
============================================
+ Coverage     10.34%   10.36%   +0.01%     
- Complexity     3417     3432      +15     
============================================
  Files           674      675       +1     
  Lines         94621    94574      -47     
  Branches      15906    15870      -36     
============================================
+ Hits           9788     9801      +13     
+ Misses        83468    83399      -69     
- Partials       1365     1374       +9     

Impacted Files	Coverage Δ	Complexity Δ
MekHQ/src/mekhq/campaign/force/Lance.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
MekHQ/src/mekhq/campaign/io/CampaignXmlParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
MekHQ/src/mekhq/campaign/market/UnitMarket.java	2.46% <0.00%> (+0.05%)	1.00 <0.00> (ø)
MekHQ/src/mekhq/campaign/mission/AtBContract.java	18.99% <0.00%> (-0.12%)	63.00 <0.00> (-1.00)
MekHQ/src/mekhq/campaign/mission/Contract.java	43.14% <0.00%> (-0.26%)	44.00 <1.00> (+1.00)	⬇️
...mekhq/campaign/mission/atb/AtBScenarioFactory.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...campaign/personnel/RetirementDefectionTracker.java	1.71% <0.00%> (+0.01%)	1.00 <0.00> (ø)
MekHQ/src/mekhq/gui/BriefingTab.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
MekHQ/src/mekhq/gui/CampaignGUI.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
MekHQ/src/mekhq/gui/adapter/TOEMouseAdapter.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
... and 17 more

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[NickAragua]

Two minor potential code changes, good to go otherwise.

[Windchild292]

Fixed both issues and have now pushed the changes