multiple output support

TODO:
pausing, renderer switching and event filter
fix renderer switch error when using multiple output logic
add multiple video renderers example
remove output from set when deleted

TODO: widget.closeEvent
add VideoOutputEventFilter to replace EventFilter in the feature

each video renderer widget will have a event filter.
TODO: QGraphicsWidget? has the same api, events as QWidget
qml: keep the same logic as other video renderers
Merge branch 'master' into multiout
qml multiple video output support
qml: compat with qtmultimeida api, add multiple video out example
fix crash when video renderer is deleted. close first
call qpainter.end() only if it is active
use filter context drawing api

TODO:
implement QPaintEngine for different backend then remove context?
add clip path to video filter
fix arch test fail for some Qt versions
Merge branch 'text' into filter
add filter manager
check whether filter is released
filter.installTo implemention
(un)install filters and tasks in AVThread for internal use

FIXME:
for the case pause next frame, if next frame is called after timeout and
before tryPause, then current frame will still displayed and not the
next frame. which is wrong
uninstallFilter and task implementions