seafile: import seafile-server package and its dependencies

Adds package definitions for the server-side components of Seafile.

I've packaged version 3.1.7 and tested basic functionality on my home router (Netgear WNDR4300), no issues, so far.

Seahub, the web interface of Seafile, tends to be a bit slow but still usable (I'm pretty sure that's because of using gunicorn and django to serve the frontend which is obviously much slower than any HTTP daemon or framework written in pure C).

To improve performance a bit, internationalization is disabled by default which makes it possible to save some DB queries and other resource intensive operations. Adding the line below to seahub_settings.py enables language support:

USE_I18N = True

NOTE: the pull requests created by me earlier need be merged first as those are dependencies of these packages.

Signed-off-by: Gergely Kiss &lt;mail.gery@gmail.com&gt;
Tested-by: Gergely Kiss &lt;mail.gery@gmail.com&gt;