GstPhotography: add writability capabilities
Submitted by Carlos Rafael Giani
Link to original bug (#757352)
Description
Currently, the GstPhotography interface has a bitmask returned by the get_capabilities() vfunc which specifies which features are implemented and which ones aren't. However, with some hardware platforms, features may exist but be read only. It is therefore useful to add another bitmask which indicates whether or not a feature is read-only or read-write.