TWRPify: Add parts to build TWRP

Change-Id: I02d1765178dd1b43cf180342a34e3a7c98475bf2
fstab: add length parameter and tweak flags for encryption

Change-Id: I9d3897ae38cfc56ada4edc3697ed5a6dae7bd2aa
fstab: add length parameter for recovery encryption support

Change-Id: Iad3a80f8de4e7ed48472bbae824c2942307bbb2c
TWRP: pkace all recovery files in /recovery/root instead of /root

Change-Id: I42bc6dcce05a7866c0ec25da631bb0ad8532b629