Add text tooltips for medals on profile

[felipecalvo]

We should add some cues as to how to obtain a currently locked avatar. It's unlocked after completing a guide, but there's no way to know which one.

At the same time, we could show a little "For completing the xxxxx guide" text on already obtained ones.

In both cases it would require a little query as medals don't know which content unlocks them. However, they currently have an unused description field we could use for this matter.

I'm thinking of tooltips because they don't require much design thought - it's either a tooltip or it's not - but there could be other alternatives as well.