Feature/effect masking

[FiniteSingularity]

This PR adds an effect masking option to the filter. With effect masking, a mask can be selected to define where and how much to blur the source. Available mask types are:

• Crop: Crop in from the sides of a rectangular source
• Source: Select another OBS source to mask with. User can specify what combination of color/alpha channels to use.
• Image: Same as Source, but uses an image file (e.g.- png, jpeg, bmp).
• Rectangle: Similar to Crop but allows user to specify the center, width, and height of a rectangular area.
• Circle: Similar to Rectangle but the user specifies the center and a circle radius to apply.
  Additionally, all masks are invertable.