main/samba: enable usershares by default
Any user part of the "sambashare" group will be able to setup a usershare for themselves to share on the network. The configuration file for the share will be stored in /var/lib/samba/usershares
Patch taken from Ubuntu.
This also allows users to setup folder sharing from various GUI's like KDE's Dolphin and Cinnamon's Nemo (they are still required to have the samba service running).