Add New Unit Option "fuelFlatCost"

[ron-murhammer]

Addresses 4th item on: https://forums.triplea-game.org/topic/558/fuel-enhancements

Functional Changes

• New XML unit option "fuelFlatCost" which deducts cost once per turn if unit moves instead of per territory moved (especially useful for air units to simplify costs and simulate fuel tank)
• Updated logic to include new option and ensure it displays with the new route message

Testing

• Tested by editing new option into Civil War and testing
  XML

    <attachment name="unitAttachment" attachTo="elite_cavalry" javaClass="games.strategy.triplea.attachments.UnitAttachment" type="unitType">
      <option name="consumesUnits" value="1:cavalry"/>
      <option name="movement" value="2"/>
      <option name="transportCost" value="3"/>
      <option name="canBlitz" value="true"/>
      <option name="requiresUnits" value="parade_ground"/>
      <option name="requiresUnits" value="general"/>
      <option name="createsResourcesList" value="-4:Supplies"/>
      <option name="fuelCost" value="Supplies" count="1"/>
      <option name="fuelFlatCost" value="Supplies" count="2"/>
      <option name="fuelFlatCost" value="Industry" count="1"/>
      <option name="canInvadeOnlyFrom" value="transport:train"/>
      <option name="createsResourcesList" value="-1:Manpower"/>
      <option name="attack" value="4"/>
      <option name="defense" value="3"/>
    </attachment>

Before

After

[codecov-io]

Codecov Report

Merging #3244 into master will increase coverage by <.01%.
The diff coverage is 40.62%.

@@             Coverage Diff              @@
##             master    #3244      +/-   ##
============================================
+ Coverage     21.46%   21.47%   +<.01%     
- Complexity     5799     5803       +4     
============================================
  Files           830      830              
  Lines         72746    72777      +31     
  Branches      11865    11873       +8     
============================================
+ Hits          15614    15627      +13     
- Misses        55034    55049      +15     
- Partials       2098     2101       +3

Impacted Files	Coverage Δ	Complexity Δ
...games/strategy/triplea/delegate/MovePerformer.java	73.13% <100%> (ø)	45 <0> (ø)	⬇️
...rc/main/java/games/strategy/engine/data/Route.java	55.47% <100%> (+0.61%)	52 <0> (+1)	⬆️
...s/strategy/triplea/attachments/UnitAttachment.java	41.92% <34.48%> (-0.12%)	244 <2> (+2)
.../src/main/java/games/strategy/net/nio/Decoder.java	73.91% <0%> (+1.08%)	25% <0%> (+1%)	⬆️

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