✨ Display multiple views of multiple databases

I kinda started this, but did not finish, sorry ...

Hecate's minimal behaviour for now is as follows:

1. changing views of the same database ; displayed data must be consistent
2. changing database (same view or another) ; displayed data must correspond to the new database
3. displaying a (for now empty) setting screen

1.,2. and 3. happens either by clicking on the burger menu items, or by directly typing different URLs in the browser URL bar.
Don't forget to test "there and back again" situations for 1.,2. and 3. (db1 → db2 → db1, or view1 → view2 → view1) , or to do permutations of 1.,2. and 3. (1. → 2. → 1. → 1. → 3. → 2., etc).