merge administrative nav for open badges

[davelester]

Instead of including separate navigation links in the administrative panel for badges and awards, create a new admin tab for WPBadger (possibly calling it openbadges so it's clear what its purpose is), and include links for adding badges, awarding badges, and bulk awarding badges below the menu.

[davelester]

What do other people think? It was feedback I received from a single individual, and I'm inclined to leave it the way it is unless others think it's worth changing.