Update folder structure based on latest Style Guide

[tdonohue]

Our current folder structure includes a lot of module paths that are prefixed with +.
See: https://github.com/DSpace/dspace-angular/tree/master/src/app

This naming pattern used to be the recommended one for lazy loaded folders, see: https://github.com/angular/angular.io/blob/b21c90c358129efdd55da897fb7756d44f3b65ae/public/docs/ts/latest/guide/style-guide.jade#L1252

However, in the latest version of the style guide, that recommendation no longer exists: https://angular.io/guide/styleguide#lazy-loaded-folders

We should consider simply renaming these folders to no longer include the + prefix, as that's now a non-standard folder name.

[tdonohue]

I ran into this again. Just noting here that the Angular team says to no longer prefix folders with +.
angular/angular.io#2944

Therefore, we should rename all these folders, as the + has no meaning, and looks confusing to new devs / users.

[tdonohue]

@artlowel : Realized we have an old ticket about renaming the "+" directories. Assigning to you to see if you or your team could quickly do this prior to 7.0. If you run into issues though or complications, let me know & we can reschedule this for just after 7.0.