role per webapp

[joshmoore]

Rather than having all webapps installed by a single role, each webapp should have its own role so that specific configuration can be applied. In the IDR case, the workflow would be:

• base IDR/OMERO role removes all top_links and then adds "Studies"
• mapr role adds "Genes", "Phenotypes", etc.
• other webapps can do the same.

The same type of extension is needed for the definition of filters (see MT 191)

See: #108

cc: @manics @aleksandra-tarkowska