When merged this pull request will:

• Add faction_filter component
  • Adds settings to control which factions (by name) are available in the unit and group trees
  • Close Feature Request: Module & Faction Curator Restrictions #142
• Fix invisible side buttons on initial load with empty trees
  • Simplify code for modeChanged and sideChanged events

Works well when tested with popular asset mods. Deals with the following object categorization trickiness (for Zeus):

• side of CfgFactionClasses doesn't determine under which side an object is sorted.
• editorCategory can also be used to categorize an object (although generally not used for characters and vehicles).
• group compositions can have a different faction display name than objects from the same faction.

As a result, we don't use CfgFactionClasses directly and instead scan CfgPatches units arrays and CfgGroups to find factions.