Roster browser (roster list, select/click to edit etc)

Create a screen for displaying rosters, and selecting one to load and 'edit' on the Roster Edit.

- For a first pass, loading a file from the server-side is fine; file management can be left to another task for now
- List a handful of rosters from local files (again, punt on file management for now unless you want to tackle that at the same time)
- Let user click a ListItem or control on it to load the roster into RosterEdit

For later:
- Use files/folders loaded by the user - for mobile... can Razor be deployed so it has a local app folder that's automatically uploaded?
- (file management in general is probably a separate, larger issue than this one)
- Delete a roster from Roster Select view