MetaExtension in PROJECT incompatibility

[lucananni93]

The new implementation of metadata update in PROJECT through the introduction of MetaExtension lacks the following features:

• Add to it.polimi.genomics.GMQLServer.Implementation the MetaExtensionFactory with the relative Default factory
• The method get of it.polimi.genomics.core.DataStructures.Builtin.MetaExtensionFactory returns a MetaAggregateStruct while the PROJECT operation in it.polimi.genomics.core.DataStructures.IRVariable accepts a Option[MetaExtension] which is a subclass of MetaAggregateStruct. This must be changed because it makes the MetaExtensionFactory useless...

Please, tell me if I am wrong.

Thank you!

[akaitoua]

@lucananni93 , can you fix it and close this issue.