Remove automatic Hex detection on message form field

[ohager]

Is your feature request related to a problem? Please describe.
Currently, the wallet detects if a message starts with legitimate hexadecimal characters [0-9a-z]. Since exchanges like Bittrex or Vayamos memos to be sent with a transaction, which are parsed as text messages only, one need to be careful when binary is flagged automatically.

Describe the solution you'd like
Remove the automatic detection - a user who needs to send hex format is considered a advanced user and knows what he does.