Added an entry for Reroute node in the node categories. Reroute is not a "real" node, but for users it's a bit hard to find, so a menu entry is ok for now.

Eventually a context menu for nodes could be a nicer solution: right-click on node link opening a popup with operators for the node, socket or link under cursor, including option "Insert Reroute".

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56753 954f8c5b-7b00-dc11-b283-0030488c597c