Feed overview

[kietelmuis]

Show overview of feeds and allow actions like selecting or removing a feed. Creating a new feed should be done from the attendees page since every feed is per attendee.

1. Selecting a feed
   A selected feed should take priority over a selected attendee. This should be the case since feeds are static links that require no more than one request to get the protocol link.

E.g.
webcal://talland.myx.nl/api/InternetCalendar/feed/3f9c2a7e-8b41-4d6f-9c2a-5e7b1a4d8f90/b7e1c4d2-6a93-47f8-b2d1-9c5a0e3f6b21

2. Removing a feed
   Removing a feed can be dangrous, this is because some users could have a feed pre-set by their school adminsitration. To prevent accidental deletion a confirmation dialog will be given.

The request to remove a feed is very easy, it's a basic PATCH method on /api/Settings which can be observed on MyX upon requesting a feed.

probably closes #31

[kietelmuis]

This feature has been paused for a while since feeds are missing an very important property; the classroom name. If Xedule decides to fix this issue by adding the property to feeds this feature can be worked on further again.