LatinIME: Give the spacebar a special treatment

* Add a fresh space bar icon
* Restyle it to be closer to other keyboards
* Disable long-press when in number pad mode
* Hide the active language text when not in long-press mode

Includes I27c02a35ed161c928c9062be5486b84f1d1f6ae5.

Change-Id: I49c1ac0affa617536f416f502683a97cad7287a9