Move decryption and post-processing code to MessageUtils (#141)

This begins work for offline decryption.

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Fix fulltext index update

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Close #141: Offline decryption

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>