Client : got "ui_invent" command working.
Data : added temporary place-holder models 'door_ph' and 'lock_ph',
sourced from OpenQuartz.
Game : added test_lock and test_door (for testing....)
Game : test for making the door open (go up).
Game : improved highlighting logic to ignore non-EF_SELECTABLE entitites.
Created 'shared/defs.qc' file for definitions (flags, etc) which will be
common between two or all three program VMs.
Client : renamed "ui_describe" --> "ui_highlight"
Game : test for linking the lock with the door via "target(name)" in the
entities file, and using SUB_UseTargets() on the lock to open the door.