Added OTR opportunistic pattern intercept.

When a message is received, OTRL_MESSAGE_TAG_BASE + OTRL_MESSAGE_TAG_V1 or OTRL_MESSAGE_TAG_V2
is searched for, if it is, the client attempts to start an OTR session.

Tested between profanity clients: WORKED
Tested between profanity and pidgin: NOT WORKING (not sure if pidgin checks for the whitespace)