Refactor keystore.

This CL isn't nearly as big as it looks.  It doesn't change keystore
functionality, it just moves all of the classes out of the former
keystore.cpp into their own .h and .cpp files.

Note that this is a cherry-pick from:

    https://android-review.googlesource.com/#/c/194971

Change-Id: Ide326c4f1d03984994d1bd9a76fa68d37da230dc
17 files changed
tree: b5d228663ff05f6d16b4c99b49a6d597666f8420
  1. keystore/
  2. keystore-engine/
  3. softkeymaster/
  4. MODULE_LICENSE_APACHE2
  5. NOTICE