celestia: fix install location
gstreamer: update from 1.2.2 to 1.2.3
gst-plugins-base: update from 1.2.2 to 1.2.3
gst-plugins-good: update from 1.2.2 to 1.2.3
gst-plugins-bad: update from 1.2.2 to 1.2.3
gst-plugins-ugly: update from 1.2.2 to 1.2.3
gst-libav: update from 1.2.2 to 1.2.3
gnome3.yelp-tools: add
gnome3: Add missing yelp_tools in gnome-3/default.nix
gucharmap: new package

GNOME Character Map, based on the Unicode Character Database

https://wiki.gnome.org/Apps/Gucharmap