repush.sh: Add recursive pushing of directory structures.

[vdrummer]

Added the ability to recursively push directory structures with repush.sh.

• Directories are created by pushing a template PDF and changing its metadata.
• In order to keep track of the parent directory during recursion, the push function takes the UUID of the parent as a second argument
• Files checking is now handled by a function called check_file
• "Documents" in strings is changed to "Files" as directories can now be pushed as well and the rM makes a distinction between "documents" and "ebooks"
• Counting files now takes the recursively pushed files into account