Iteration 2: Show unlocked VeraCrypt file containers in GtkPlacesSidebar

Development repository: https://github.com/segfault3/gtk
Branch: gtk-3-22_add_loop_and_dm_to_sidebar

Parent Task: #15223

Original created by @segfault on 15225 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information