I'm wondering if the UI panel is in some tab I haven't found yet or is it no longer available in the versions other than 2.77? I'm also having trouble finding the option "make proxy". It is not in the Object tab :/
Sorry for all these questions!
I don't know if the file was updated since then, or if this is just how 2.8 works in comparison to 2.77(I started in 2.79)
But the Rig UI's is visible in the tool bar only when you are in pose mode.
In case anyone was looking for it still.