epic: continue launcher clean-up

[skaldarnar]

Follow up to #612 to cleaning up more stale code. If this PR becomes too big and complex I'll split it up into smaller parts which can be reviewed and merged separately (one after the other).

Changes

• chore: remove unused properties from Settings
• chore: flatten gui.javafx package to ui
• chore: clean-up LauncherVersion
  • rename TerasologyLauncherVersionInfo >>> LauncherVersion
  • move LauncherVersion to model pkg
  • simplify instance creation of LauncherVersion
  • remove unused properties gitBranch, gitCommit, ...
  • ... and eventually get rid of Properties
  • build: generate version.txt to resource build dir