merge disco plugins

[flosse]

There are two service discovery plugins with different APIs. We should either merge both plugins into one or refactor the APIs so that they are equal.

• https://github.com/metajack/strophejs-plugins/blob/master/disco/strophe.disco.js
• https://github.com/metajack/strophejs-plugins/blob/master/disco/lib/strophe.disco.js

[mweibel]

imho the 2nd is far too complex code for such a small feature ;)

[flosse]

Moreover the 2nd one depends on jQuery. So we might use the first as a base and "copy" all other missing features from the 2nd one ;-)