add ChatForm:ClearFace()

Not added to ChatForm:Clear(), because scripts typically want to set the
face once for the entire Player/NPC dialogue, but clear the other chat form
contents for each dialogue node.
clear face when switching to candidate crew list. fixes #2647
modelviewer: display the ship's bounding box with the collision mesh
Merge remote-tracking branch 'johnbartholomew/modelviewer-show-aabb'
Merge remote-tracking branch 'johnbartholomew/issue-2647'
ocd fix
auto-commit: translation updates
move cameraZoom{In,Out} key bindings to a 'General View Controls' section
add English translation token for 'General View Controls'
declare key bindings for all the SectorView controls
add English translation tokens for all new Sector View key bindings
hook up all SectorView key bindings
Merge branch 'johnbartholomew/sectorview-keybindings'
SectorCache::ClearCache to completely clear cache.
Do not assign factions to sector when called from Faction code.
Avoid instantiating Sector directly for calculating distances.
Make sure there is only ever one Sector object for each sector.
Move exploration state to Sector::System
Allow unexplored systems to become explored in game.
Persist explored state of a system.