Mecha, hud, and click fixes

These are probably late sorry
* Fixes #1487, drilling your inventory
* Fully prevents inventory use while in a mech
* Hides your inventory when you enter a mech, you can reveal it with F12
* Better fix for #1164, the E (quick equip) gui button now works as it should, instead of hiding the newly equipped item
* Ghosts can shift- and alt-click, meaning you can still examine with inquisitive mode turned off, and you can use the new alt panel to look at densely packed squares.