[Feature] extending the MEMO feature in Peerplays

Right now, ie by default Peerplays blockchain is allowing memos to be send only as encrypted messages.

We need an option to send plain text memos as well.

Feature description:

• A message with the character # at beginning should result in encrypted messages
• A message without the # should be a plain text message (visible publicly on the chain.)

This is required for simplifying the Hive SONs process.