Add customizable facets dialogs

[archymedes]

It would be useful have a tab for customizing facets parameters like background box, size and text color. Maybe it could be placed in "Panel & Background" or even in "Title and label".
PS: "Title and label" text tab should be capitalized and using "&" instead of "and" like "Panel & Background", resulting as "Title & Label".

[calligross]

I added support for strip.background and strip.text.

Please install the dev version from GitHub and check if everything works. Thx!

[archymedes]

I've checked the dev version and it works like a charm. New features working. Thanks for your hard work that simplify ours.