WIP: Add new remote-sync plugin

This implementation aims to support synchronizing songs, custom slides and services files, though only songs are currently supported.

The idea is to define a "framework" where it will relatively easy to add new backends. Currently there is one (mostly) working backend, which uses a simple folder structure (the folder could be placed in dropbox or SMB/NFS share). An untested backend that uses FTP is a simple extension of the folder based backend.

The main files to look at are: openlp/plugins/remotesync/remotesyncplugin.py openlp/plugins/remotesync/lib/backends/synchronizer.py openlp/plugins/remotesync/lib/backends/foldersynchronizer.py

There are some todos:

• Implement sync services
• Implement handling of detected conflicts.