scale down ring icon

For some reason certain system trays (panel indicator applets) are
not able to properly scale the current ring icon, resulting in very
large panel icons.

This is a scaled down version (16x16) of the original svg with the
adobe binary stripped out as well.

Change-Id: I3e2190653a1154ae44f28dbafa9ebd299df793d4
Tuleap: #839