Add support for DocumentLibrary requests.

Mimicks EAS' ability to browse/download resources specified by a UNC locator.

For Horde, this basically means downloading files via the "files" API. Very few
clients support this fully. My Note 3 allows only specifiying an explicit file (no folder browsing).

Files should be specied as \\{backend}\{user}\path\to\file.txt where {backend is the gollem backend, e.g., 'file' so:

\\file\mike\picture.png

Of course, this relies on the gollem/files API to actually work - which is currently missing perms checks.
Implement DocumentLibrary support in Core.
Add missing files.
Update package.xml
Update package.xml