Implement permissible file integrity verification

Implement permissible file integrity verification

Permissible files have a SHA-1 hash attached at the beginning.
Upon opening it is compared with a new hash calculated from the
file content in order to verify if the file's integrity is intact.
An error is thrown should the hashes differ. Files with no hash are
still supported but reading/updating the rules stored in them
will cause them to automatically switch to the new system.

Change-Id: I5ec379b58cc78e63bcde084ada43273237d61beb