svn: convert into a module

I have removed the svn::groups class as svn is only served readonly, and it
seems it can be removed.

I didn't include init.pp as it seems redundant here.
also removed the apache dependency for the time being until the status
of this service is cleared out.

- move server.pp to init.pp
- rename svn::server to subversion and svn::client to subversion::client etc
- adjust file pathes
- add role class
- minor lint stuff like line over 80 chars and aligned arrows

Change-Id: Ife6ab663edba01ecd86977ae13a3838f3979e2ed