Allow locking the base chassis of an Omnimek

[pavelbraginskiy]

To make it easier to build new configurations of existing OmniMeks, this makes it possible to prevent all modifications to the base chassis while allowing pod equipment to be altered.

This should prevent modifying any of the Mek's systems, removing or moving any fixed equipment, adding any equipment that can't be pod-mounted, or adding any equipment as fixed equipment.

For now, only OmniMeks are supported. OmniVehicles and OmniFighters will hopefully be covered in the future, but admittedly my desire to work on those is completely tapped at the moment.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 2.12%. Comparing base (d8c7c57) to head (9977dea).
Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##             master   #1712      +/-   ##
===========================================
- Coverage      2.13%   2.12%   -0.01%     
  Complexity      209     209              
===========================================
  Files           271     271              
  Lines         31393   31520     +127     
  Branches       5342    5366      +24     
===========================================
  Hits            670     670              
- Misses        30566   30693     +127     
  Partials        157     157              

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[repligator]

Gladiator (Executioner) Prime (ID 1211)
I can remove the (fixed) heat sinks by pressing up or down on the Structure/Armor tab under heat sinks.

I'm also getting an NPE when right-clicking on limbs under the Assign Criticals tab.
java.lang.NullPointerException: Cannot invoke "megamek.common.CriticalSlot.getMount()" because "cs" is null
megameklab.log

[pavelbraginskiy]

The fact that the total number of heatsinks can go lower than the number of base heatsinks has always been an oddity, but I it'll be good to get that patched up anyway.