Provide a simple way to reconfigure desktopcouch when storing design document on filesystem

[Adi Roiban]

As described in the „Storing design documents and views on the filesystem” wikipage, after a design document is changed on the filesytem, desktopcouch needs to be restarted.

http://www.freedesktop.org/wiki/Specifications/desktopcouch/Documentation/DesignDocsFilesystem

Restarting desktopcouch is not a trivial task, as it required to kill the current erlang process, remove the ini file and issue a dbus signal.

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Maybe we can have a simple dbus signal to request reloading the design documents

Sending the signal over seesion dbus is useful for development.

I am not sure what is the best way of reloading the design document when installing or upgrading a package.