Updated holsterable items

Changed holster definition lines (SetItemTypeHolsterable) to regular
code rather than a loop for weapons. Removed some weapons from the
holster ability.

Added the Taser and Shield items to holster list, these items can now be
holstered just like weapons.

Added code to protect the player from damage from behind him if he has a
shield holstered.

Increased the level of protection offered by the shield to 90%

Fixed a bug where action text wouldn't disappear when picking up
weapons.

Finished up some vehicle code loose ends from the last repo commit.