Mecha fixes

Prevents mech actions from acting on the user's inventory.  Fixes #1487.
(Almost) fully prevents inventory use from within a mech, to be more consistent.  The internals GUI button still works on the theory that it's emergency equipment.
Mecha HUD hiding

Hides the user's inventory (as per F12) when they enter a mecha, since it is essentially unusable.  Pressing F12 will reveal it, as will exiting the mecha.  If your inventory is hidden before you enter the mech, it will remain hidden when you leave.
More correct fix for #1164 that does not introduce new bugs (oops)
Re-adds the ability for mobs to turn when clicking on a wall object in their square (APC, etc)
Re-adds ghost shift- and alt-clicking, sorry about that.
Removed a colon from APC code on a really weird case of MALF AI YAY THAT SHIT

anyways it won't runtime anymore
Fixes landmark for plaguedoctor costume not spawning the mask.
Lame.
Fixes #1591 by setting the default icon_state to an icon state that actually exists.
Merge pull request #1589 from SuperSayu/clickstuff3

Mecha, hud, and click fixes
Merge pull request #1639 from Intigracy/doesanyoneevencarewhatInamemybranch

Fixes landmark for plaguedoctor costume not spawning the mask.
Merge pull request #1645 from AndroidSFV/fix1591

Resolves #1591
Merge pull request #1631 from Aranclanos/MalfAIAlwaysScrewingUpThings

Removed a colon from APC code. Just one. Nothing else.