Load From File message

On Linux when the user presses cancel on the "Load from File"
dialog, was getting an error message saying the app could not
open the file.

Also fixed a spelling error in ApmPlaneLevel.cc.
Merge pull request #51 from kellyschrock/master

Load From File message
Changes so UASQuickView item selection dialog now uses a list for selecting item categories to add/remove from the view
Updates to the layout of Install Firmware view. 
Provision for new reboot button.
Some improvements to error handling.
Minor visual improvements to the Radio Calibration Screen