Add ability to view the schedule of other people

[arthurrump]

There's a draft. What to do next?

• [x] Navigate to the added page
• [x] Don't cache ScheduleView, but save state per user (or other 'schedule owner')
• [x] Handle back navigation properly. Currently navigating back to any SchedulePage will set the HamburgerMenu to the main one
• [x] Add ability to close a ScheduleView from the HamburgerMenu (and also strip it out of the back stack)
• [x] Improve UI on OtherSchedulesView, with a list of available students/teachers/groups/locations
• [x] Improve UI on ScheduleView to detail whose schedule you're looking at

[20170706] Aaaand don't forget:

• [x] Implement viewing schedule for groups
• [x] Implement viewing schedule for locations

The navigation/hamburger issues might be best solved by using a custom NavigationService and HamburgerMenu (maybe with the one from UWP Community Toolkit, which doesn't have build in navigation).

[arthurrump]

The HamburgerMenu actually tries to match the pageParameter... But in v1.1.12, the one that's on NuGet, it matches the pageParameter to both the value ánd null, then selects the first one, which is the one being null. It's fixed in master, though. Workaround: set the pageParameter to ~me for the main one.