Allow for easy switching between Collectives

[cb109]

It is currently quite annoying when switching between collectives, especially with using the app from a homescreen icon.

It would be nice to store tokens for all currently logged in collectives and allow for a quick change. One way to do that could be by scoping all localStorage values by collective id so that we can store as many as wanted next to each other.

[cb109]

Changing still needs to logout and log back in, but by displaying visited Collective names and giving a back-button on the login screen this is already much easier now.