Feature/Pull request: Payment confirmation when hint is not free

I recently played in a ctf which used the fb platform, and I found it very convenient and easy to use indeed.

However, I noticed that you are always one click away from losing points by accidentally clicking the "request hint" button.

Additionally, the amount is displayed only on mouseover, so you are already half way there.

As you probably realised, when playing the ctf, I clicked on a "paid hint" button I didn't intend to. I whined a bit, and now I want to submit a pull request to improve it by adding a simple confirmation "dialog".

I already experimented with the code, and developed the feature. If you think it is a good idea, I will submit a pull request.