Added boarding ai modification...

...fixed a bug with linking of mounts to gibs during loading
Added convenience methods to Directions enum
Added prop visibility inheritance flag...

...fixed a bug with props not being hidden when the parent object is
deleted
Missing file from commit 86ce6e98fa8287aebcfeb28e48c430bec618e3c1
Changed gibs classes to extend image classes
Misc minor changes...

...fixed a bug that would not allow the user to confirm selection of a
drone list,
selection dialogs now scroll to always show the selected item
Changed mount direction arrows to use props
Added dispose listener to addTooltip()