Topic/instance switcher

Opening this at Mike's request. The feature basically works, but there are a few fatal crashes that I'm still working through, which will get fixed before this is merged.

Please disregard the first two commits, they mirror each other. This was used as a way to check in inbetween changes, but continue to edit them in the staging environment, by backing them out. This will not be merged.
Consider giving this and `white_with_dark_gray_border.xml` more semantic names like `instance_switcher_header_border.xml` and `instance_switcher_element_border.xml`, and moving the color references into `colors.xml` with semantic names there as well.

Also, you should use the same background colors as the rest of the app (I think it is `@color/main_background_color`?)