This adds encryption to Spigots app

It adds AES256 encryption with an SHA1-HMAC verification, and PBKDF2
key stretching using SHA1.

Also adds UI for encryption (passphrase input, etc.)

BUG=chromium-os:19697
TEST=exported and imported encrypted ONC files.

Change-Id: I7d39788c7e511ae2d22f8633f3cfd270dbdea295
50 files changed