File details (fixes #64)

OK. This is a biggie, as it turns out.

This adds viewing of file details to the long press menu for files.

This file details screen contains historical versions as well as a toolbar to perform some of the sharing, downloading and favoriting functionality that the long press menu has. This meant refactoring those functions out of the file item view and into a parent view that both file items and file details extend.

This PR also includes some new font icons and tests for the new model and collection.