[Qgis-community-team] new repo in the installer

[Borys Jurgiel]

Just to let you know that I've added Volkan's repository to the defaults ones in 
the plugin installer, as it seems to work stable from the beginning. You can 
click the "Add 3rd party repos" button to add it.

In the autumn we will need to finally implement the proxy in the main 
repository, so the authors' ones will could be dynamically plugged and unplugged 
in case of any problems.