Media Theme deployment should be able to handle themes from Gallery

[humanoidcreature]

I.e. it shouldn't handle just zips, where the Theme.txt can only be one folder deep, but we add support especially for the Gallery (where is a zip with .nupgk file extension, and also the theme is in a certain folder inside the package).

Problem is that inside the Gallery themes there are cshtml templates, which aren't usable on DotNest.

[Piedone]

We can't do this without cshtml support, which we won't have.