Integrate user manual and install guides into KA Lite

Not mergable yet, needs polish

Foundation has been laid though, to do list includes:

1. Migration for the new user resource model
2. Navigation and styling for user resources and user resource detail page
3. Linking from the main KA Lite page in the appropriate places (not just in download section) 

and other things I'm sure I'll think of tomorrow 
This is brittle. Use `StrictVersion`. Here's an example: https://github.com/fle-internal/ka-lite-central/blob/master/centralserver/central/api_views.py#L66