Add command line capabilities

Allows sending openrecoveryscript commands to TWRP via shell.
This may be handy for visually impaired users, for various one
click utilities to drive TWRP commands from a computer, for using
TWRP when a catastrophic hardware failure like a shattered screen
prevents you from being able to use touch, or even on devices like
a TV stick where touch and USB mouse input is unavailable.

This patch also includes a few minor changes to openrecoveryscript
including proper support for rebooting via the script and for
decrypting the device via the command line.

Change-Id: I796ad168efdd2da9c25334ac93d1079daaa7b0bc