Implement folder hierarchy for filing & Attach Articles to PDF file

*All Folders and Items now have an instance of File, to store folder
locations and filepaths, respectively.

*They each also have a constructor which takes in "File loc" which is
used to allow objects to inherit its superdirectory location from the
instance of Folder inside of which it is created.
	*Folders inherit their own directory name via "label"
	*Files inherit their filename via "title"
	*TODO: file extensions?

*Once Cabinet is an extension of Folder, the only object which needs
an absolute location is Cabinet—others will inherit its file structure
from the parent folder

Signed-off-by: jnickg <jnickg83@gmail.com>
Delete Book (for now)

Will be implemented LATER