Integrated 56812d2255d7c4ebd711e8aad8c603be01158915 from M1cha:
add dualsystem support
show system-selection before confirm to install zip

Change-Id: I26b98233a8764b7c6a29977c70dbe75b11763362
(cherry picked from commit 404e988d91cb9387192226bc6bd89481fc90a9f8)
Integrated 4be89a62845506af92dbe66fc77b11a671b51c13 from M1cha:
verify_root_and_recovery for both systems
Integrated 6a009a07ffb4cbb3f7a18a6f5cb3115ab6df1a82 from M1cha:
add advanced option to change bootmode(system0 or system1)
Determine /misc partition through fstab, make it work on the Mi3
improve function set_active_system

Change-Id: I1623abc4e54a04f7c82876cf0ae8fb538b0b2e6a
Partly integrated 699c7263ab25c6ee84870c08f07c6722b81e6248 from M1cha:
- fix: backup/restore boot1
- fix: ask user to select system for advanced restore of boot and system
- optimize: only show existing images in advanced restore menu
Set default storage location to /sdcard/0:

  - clockworkmod data location (e.g. nandroid) is /sdcard/0/clockworkmod
  - default update.zip location is /sdcard/0/update.zip
remove bogus line left over from TDB code