MyChat Scripts Engine: working with messages

Functions to edit and send messages to MyChat Client.

mConvertMsgToPlainText	convert message text to plain text with no tags. markups and special characters;
mExtractExternalWebLinkFromMessage	get the external http(s) link on a file from a message;
mSendCustomMsgToClientConsoleByCID	send a special message to MyChat Client console;
mSendPrivateMessage	send a private message on behalf of one MyChat user to another;
mSendPrivateTechMessage	send a technical message to a private conversation between two users with no sender and entry in the message history.