Bug 915312 - Part 4: native implementations of PBKDF2 with SHA-1 and SHA-256.
Clean up NativeCrypto.java.
On-device PBKDF2 tests.
Bug 915312 - Part 5: expose NativeCrypto.scrypt.
Bug 915312 - Part 6: add Scrypt and PBKDF2 interfaces.

This also adds testing only implementations backed by SpongyCastle.
Bug 915312 - Part 7: add Crypto class to implement PBKDF2/Scrypt interfaces.
Bug 905433: First version of PICL key stretching.
Bug PRE: add BaseResource.post(JSONObject).
Bug PRE: add HKDF.derive helper.
Bug SRP: Add SRP constants.
Bug SRP: add SRPConstants.hexModN helper.
Bug SRP: implement FxAccount.