Would be nice to support filters

[Jean-Francois Dockes]

Ok, this is not a bug but a feature request, but I can't seem to find the right place for those...

The Simple Unity lens builder and SingleScopeLens do a nice job to isolate the lens code from most "complicated" stuff, but it is still necessary to access Unity for using filters, which are not really an "advanced" feature. Specifically you have to:

  - Use Unity to create the filter, something like: filter = Unity.RadioOptionFilter.new("rclcat", "Category", icon, False)

  - Guess that the filters should be installed as Meta.filters (doc lacking)

  - Access the "hidden" scope to retrieve the filter value: fcat = self._scope.get_filter("rclcat")

A little additional wrapping and/or documentation would be nice :)

[quent57 (quent57)]

I'm completely ok with this comment.

I purpose a very simple patch in order to be able to access filters in the same way than categories.

I'll try to create wrappers for filters and do some doc.