[UI] Introduce option to enable full selection annotations

Since there are no "full selection annotations" yet, toggling the option
has no visible effect in a Saros session.

Change-Id: I2d44e1415a26c581f8d25eaac50a52d3aa0f577a
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1241
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>