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

Minor updates to the graph functionality

Changed order to draw the target line first, and then the actual line so this line is shown above the target line.
Graying out graph when it's offline.

Updating target temperatures in UI based on gcode

Temperature graph

- update French translation
- store elapsed time since the actual beginning of the print to make ETA non crazy when pausing in the middle of the print
- handle another exception which happens when the printer gets disconnected

Merge fixes added to master into experimental

Modified wildcard for FileDialog to add an choice to show All Files

preview zoom by key

zoom big preview by shift + key

Minor fixes