Qt: update to 5.3
Ground/NewsPanel - Added author avatar and link
GCS/Welcome plugin - renamed NewsPanel to GitHubNews and added ForumNews
makefile: filter ARCHFLAGS env var from user environment

Unexpected values in this variable can cause strange compile
failures.
Merge pull request #1205 from solidgoldbomb/sanitize-archflags

makefile: filter ARCHFLAGS env var from user environment
Merge pull request #1202 from guilhermito/welcomePlugin

Welcome plugin
Qt5.3: fix path to windows qmake and dlls
Qt5.3: remove duplicate usb method definitions

These were removed from some versions of mingw but no
longer need to be redefined.
Merge pull request #1198 from peabody124/qt5.3

Qt: update to 5.3