Add a tracks page that shows which modules are in which track

[Matt Stauffer]

My current idea:

Table:
Each column is a track
Each row is a module
Checkbox or whatever to match each track to the modules it

Note: Currently there are three tracks but we may eventually (or even soon) have 4-5, so try to build with that in mind

[Matt Stauffer]

Probably lives at /en/tracks