Need for gemoc version specific discovery repositories

The current discovery (ie. install additional GEMOC component button) use a single xmi file
This does not take into account the fact that the provided components are compatible or not with the studio.

For example, http://kermeta.org/gemoc-ale-execution-engine/updates/2018-06-15/ is compatible with GEMOC studio 3.0.0 but not with 3.1.0

It would be better to have a different discovery catalogue for each version of the studio. So each catalogue would point only to valid update site for the given studio.

the counterparts are:
* we potentially need to duplicate the information.
* how should we manage components that are not compatible anymore? if we simply remove them, a potentially interesting component will not be advertised and we may "forget" about its existence...