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.
Param Write UI confirmation

Add logic to provide a visual confirmation of parameters
written to the UAV when the "Write" button is clicked.

Also, display a count of parameter differences between
the current settings and a just-loaded file.

Also changed the highlight color in the grid slightly to
make it easier to see the values when using the indoor
mission style theme.
Merge branch 'param_write_ui_confirm'