Integrate overlay explanations of controls

[bestchai]

Current interface is far from self-explanatory. It would help to have overlays that (1) highlight interesting parts of the page, and (2) explain what they are/how to use them.

One way to do this is through the open source pageguide project:
https://github.com/tracelytics/pageguide

It seems non-intrusive and would integrate well.

[Issue created by bestchai: 2016-07-11]