OpenSync plugin for Claws Mail

This plugin acts as a data server for Claws Mail's
addressbook and calendar. It acts as an interface
to both data sources for external programs.
Information about contacts or events can be queried
and/or modified. This plugin needs to be loaded
if Claws Mail is supposed to take part in an OpenSync
synchronisation group.

It also acts as an additional safety net when doing
synchronisations (it can be requested that any
modifications in the addressbook or calendar need to be
approved), and allows to configure some Claws
Mail specific parts (for example, into which addressbook
new contacts are supposed to be added).

This is alpha software. Be sure to back up your data
on all sides of the sync group before trying this out.