Removed option to send private message if it would go to system. Closes
Removed pm symbol if sent by own user
Added one time binding to ng-if
Removed extraneous space
Merge pull request #4295 from crookedneighbor/do-not-send-private-messages-to-system

Removed option to send private message if it would go to system. Closes #4295
Allow send messages to yourself - see #4295
Adjusted ng-hide so users cannot block themeselves