Update README

Update the readme to refer to the diydrones location.
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.
Use C++ style cast instead of C-style
CH6 Tune segfault fix

Kept getting segfaults when setting basic PIDs upon clicking
"Write Params". Looks like the wrong combo box index was being
used for the "TUNE" parameter.
Fix to Radio Channels PWM values to use a dark colour when 'outdoor' style is selected.
Added warning dialogs to pre flight commands that can cause a vehicle to crash if not on the ground.
Fix for selecting trunk firmware changing the name of the beta firmware button
Fix for #52, where PX4 upload thread didn't exit properly on an error condition involving unplugging the device in the middle of flashing