Fix print button, add tooltips, add icons to layer preview

Ignore "wait" messages from spammy firmwares and show timestamps with received messages (courtesy of juri_)

Use system default for the background color of plater/compose function.

Update stlview.py   Double-click on window attempted to load a potentially non-existant stl file. Now prints the location and window name.

Closes #174 - Correct layer-count when z is lifted for travel moves

Merge branch 'experimental' of https://github.com/jezmy/Printrun into experimental

Conflicts:
	gviz.py

Layer info display merge

GCode viewer now displays layer info in status bar when scrolling

Destroy file selection dialogs after use - fixes a memory leak as well as a gtk bug that vim triggers when editing gcode files

Merge experimental back into master