UI, TRScenario, less verbose log

- UI for per-Kerbal head and suit assignment added to Space Centre
- per-Kerbal texture assignments are moved to TRScenario inside individual games
- CustomKerbals configuration only is only used to initialise TRScenarion when
  added to new or existing games
- less verbose log output, texture mappings omitted
Stock suit fixes, icon added

- fixed atm. IVA suit when using stock suits
- fixed displaying of stock suits in UI
- added toolbar icon
Fixed CustomKerbals overriding, doc updates

- fixed CustomKerbals overriding with missing headTex/SuitDir
- updated README
- prepared for release
Fixed back button

- fixed back button skipping last texture when the default one is selected