Tree - add find node by regexp/substring

Fixes #29
Added server roles support

Adds classes/methods for setting up server roles in configuration -> settigns.
The whole configuration section has very dense and deep structure - this patch
attempts to reflect this by adding directory/file structure which will allow us
to add more config pages in future without causing too big mess.

Fixes #11
Merge pull request #33 from jprovaznik/serverroles2

Server roles