Add a configuration options for mobile plugin in the Mobile Messenger.

I would like the options to be always present in the settings screen, however, if the server does not support them, they should be inactive. If the server supports them (tigase.org, tigase.im) they should be active. The support should be "discovered" using service discovery mechanism.

I am not sure who is the best person to implement it, I am assigning it to Andrzej as he is the author of the plugin on the server. However, if you think it is more appropriate to assign it to Bartek, do not hesitate.