Graph View: Fix for UI not refreshing, and added MODE string messages

@rolandbosa suggested an implementation to allow for MODE strings to be
displayed on the graph. While I couldn't directly pull in his change, I
have reimplemented the MODE display as he recommended.

There is also a small fix for the plot not updating properly twice a
second when it is on screen.
Graph View: MODE string messages now display for live  data and tlog replay
Build: Changed debian rules file to include APP_PLATFORM defines for pbuilder