Introduce RssFeedViewModel

Furnishing the RssFeed function as a single activity with fragments for
Manage and Import.
3 jobs for !1366 with 1894-viewmodel-for-rssfeed-activities in 10 minutes and 31 seconds (queued for 3 seconds)
latest detached
Status Name Job ID Coverage
passed test #9405


  Optional Tests
manual android test #9406
kvm allowed to fail manual
manual bridge test #9407
allowed to fail manual