Check for null.
Merge pull request #86 from jlewin/development

Account for null reference condition when assigning .ActivePrinter - Fix...
Change start button to "print"
Merge branch 'development' of https://github.com/MatterHackers/MatterControl into development
Don't change queue selected index when printing from library or history if item is already printing (or paused).
Merge branch 'development' of https://github.com/MatterHackers/MatterControl into development
Rename printer model.
Revise EEProm form