build-pac.sh: Save snapshot of tree

  Add default snapshot and option to restore snapshot sources
  Upstream commits routinely break a previously successful build.
  This commit easy restoration of the last build tree

Change-Id: I091947e2ebab1c322381601bbff4e5ba41340857
vendor: add option to build TWRP Recovery [1/2]

ps1: this is proof, not merge
ps2: update message
ps3: set by default cwm, then it will be overwritten if you use TWRP

Change-Id: Ifc70277c294e1434603962bc6d8663b0c314fa68