Instead us a Toolbox concept which hangs off of QGCApplication

Removed "Clear Text" context menu from roll down dialog
Fixed "Clear Text" context menu in Info Dialog (renamed to "Clear Messages" in the process)

Shrunk the Message drop down dialog a bit.
Made the Message drop down dialog slightly transparent.

Right-click menu works cleaner.
Coloring of output text is correct.
Output text now handles all severities of messages.

Anton and I noticed that the message view stops autoscrolling properly
sometimes when there's a high frequency of arriving messages. This
should fix that problem.