DirectShow: refactor custom renderer filter

Refactor out some of the filter and pin logic into the
DirectShowBaseFilter and DirectShowPin abstract classes.
This will avoid code duplication when implementing the probe
filter. The existing source filter (for qrc files) can also be
refactored to use these abstract classes.

Change-Id: Iaf141472dea82579ad085b3318624f9a57aa46d8
Reviewed-by: Christian Stromme <christian.stromme@qt.io>