Don't return trashed collections from `/users/:userID/collections` by default

[dstillman]

Add includeTrashed support

@tnajdek, what does web-library do about this now?

[tnajdek]

We always pre-fetch all collections in a given library in order to build a complete tree/child map (that's why libraries with a large number of collections show a loading meter when the web library is first visited).

With all the collections at hand, web-library filters deleted collections out of the library's tree view. Instead, these are injected into the trash view. This was first implemented in 2ae0a6ff.

If the dataserver stops returning trashed collections for this endpoint, web-library would simply stop displaying them in the trash (but, hopefully, nothing else would break). Ideally, I could patch web-library to fetch trashed collections separately, and we would sync the deployment of both changes.