Move path preview removal from inventory state to inventory button

because seems a neater place for it.
Fix inventory button in debug mode not always resetting TUs

Currently you need a unit with an inventory screen to reset TUs.  A lot
of aliens do not have an inventory screen so if there is no convenient
alien around you are stuck.
Fix displaying stats for wrong unit during debug turn.

Updates stats while watching aliens move; currently seeing stats
for the previous alien.
Also when you get to play aliens ensure that the stats for the
currently selected alien are shown; again previously moved alien
stats are displayed.
Merge pull request #772 from cfailde/debugInv

Inventory and debug fixes