big commit

important things:
- ICMClient is now observable, and set to publish anything it receive
from the server -> observers will decide what they want from it.
- intent handlers now require ConnectionToClient as second parameter for
execute method.
- login working for user.
- browsing user mail working too.
- UserInboxComponent no longer takes UserMail[] as parameter; mails can
be added one by one using addMail( UserMail ).