Automatically add all the UAVOs to the GCS project

Pro: No more hassling with GCS when adding a new UAVO. This is especially nice for inexperienced developers because the compiler error when a new UAVO is not included in ```uavobjects.pro``` doesn't provide any hint about how to fix the problem.

Con: This indiscriminately adds all .cpp and .h files in the directory. Currently, there are no files beyond UAVObjects, but this makes that a de facto requirement. It also means that a deleted UAVO will continue to be compiled (since it will always exist in the UAVOBJECT_SYNTHETICS directory until a make uavobjects_clean.

Partially fixes https://github.com/TauLabs/TauLabs/issues/231.