Issue 535 fix

This fixes the warnings described in Issue 535. All were uninitialized variables.

I have also included a new command line CONFIG+= switch called WarningsAsErrorsOff which provides a quick way to locally override. I updated the comments in QGroundControl.pro to describe the process of how to handle warning errors:

"We treat all warnings as errors which must be fixed before pull requests are approved. If you run into a problem you can't fix you can always use local pragmas to work around the warning. This should be used sparingly and only in cases where the problem absolultey can't be fixed. If you run into problems in code which is not yours, please lend a hand and fix the issues. If you don't have time for that post an Issue with your OS and compiler information as well as the pertinent output from the build log. If it's a problem that will take longer to fix, we will temporarily turn off warnings as errors for that specific config until the Issue is taken care of. Once that is completed we will turn warnings as errors back in for the config. You can use CONFIG+=WarningsAsErrorsOff in your private builds for a quick local override. Please report any problems you run into with warnings as errors so we can gather information on its effectiveness as well as its annoyance level."