MUC create / search doesn't handle extraneous prefix/suffix well, error message unclear

[StuartJMackintosh]

Movim v0.20rc6

When Movim is set to handle XMPP links in the browser, clicks on MUCs such as from https://search.jabber.network/rooms/1 with the convention 'xmpp:[email protected]?join', Movim appears to handle as expected.

However, observing recent user behaviour, when copied and pasted in, say when the MUC link is copied from the page, the search does not return a match. Users then may then decide to manually add this chatroom.

Then if manually added as custom MUC, the error 'Your Nickname is not valid' is displayed when the bookmark selected.

Once the bookmark with extraneous data (prefix "xmpp:" suffix "?join") is saved, it seems to also prevent the bookmarks from synchronising with the server until it is deleted (Have not replicated this).

To reduce the chances of user surprise, I propose:

1. Strip the extraneous information from the bookmark when created as custom MUC
2. Strip the extraneous information from the requested MUC when searching
3. Improve the error message when a MUC is invalid

[edhelas]

Related to #492