Index: Make the buttons clickable.

Very ugly code at the moment because code is duplicated but it works. I'll make another PR that will make use of code reuse.

Screencast: http://gfycat.com/CircularShadowyBluejay
I think topics ids aren't the same for everyone, it depends on the order in which they're added to the database.

For example on my instance "Productivity" has id 1, math & science is 4, etc.