Clarify differences between "internal" and "common" Ajax views?

[mikkonie]

As of v1.0, the projectroles app features two "common" Ajax views intended to be used by SODAR Core based sites if needed. These are SidebarContentAjaxView and UserDropdownContentAjaxView. Other Ajax views, however, are intended to only be used by existing projectroles views.

We probably should make this difference more clear by e.g. separating the "common" views into a separate module, or at least a clearly separated section within the existing module. This is also to remind us developers that making changes to these views may cause issues.

Also, one option would be to simply change these into "real" REST API views and have them follow a relevant versioning scheme.

Not major or urgent IMHO, but opening the ticket so this can be thought about.