Add librem.one as default jabber provider
A tentative solution until GOA is available, to suggest using a librem.one jabber account
- When adding a new account, the radio-buttons for selecting the protocol won't show up if no other protocol plugins than XMPP are available
- The account name is split into user_id and the provider portion. The new text-entry for the latter is preallocated with "librem.one"