Add WebVfx filter (WIP)

Conflicts:

	src/docks/filtersdock.cpp
	src/docks/filtersdock.h
	src/docks/filtersdock.ui
	src/models/attachedfiltersmodel.cpp
	src/src.pro
Fix multiple shotcut filters for mlt filters.

For example, webvfx has multiple Shotcut filters. So, we need to select
the correct UI (where possible). The filter's unique ID needs to be
expressed through the objectName property in its metadata.
Add Overlay HTML filter with WYSIWYG editor.
Update translations with new strings.