Add an option to forward sms to the stock database

Created by: c33s

for better integration with other apps like condi or tasker (for unmuteing the phone,...) it would be great to add an option to forward specific messages to the stock sms app.

maybe having a checkbox to choose which type of messages

• all (decrypted and unencrypted)
• unencrypted (crypted sms which will be forwarded crypted)
• plain (unencrypted sms, which never have been crypted)
• decrypted
• (maybe from a specific number or group)

edit: messages containing specific words, no matter what their encryption state is (like "unmute") gets decrypted and forwarded to the stock app

split from issue https://github.com/SMSSecure/SMSSecure/issues/144