app: cleanup KDevelop namespace

using namespace instead of KDevelop::
debuggers: cleanup KDevelop namespace

using namespace instead of KDevelop::
formatters/astyle: cleanup KDevelop namespace

using namespace instead of KDevelop::
formatters/customscript: cleanup KDevelop namespace

using namespace instead of KDevelop::
kdeintegration/kdeprovider: cleanup KDevelop namespace

using namespace instead of KDevelop::
kdeintegration/executeplasmoid: cleanup KDevelop namespace

using namespace instead of KDevelop::