No more locks

I've been trying to figure out what the model for moving ahead with assignments should be, and have become convinced that it's best to let the user decide when they're done.

A lot of people don't quite "get" the idea that it's not a race, and that it's about having an interesting discussion... but that's entirely my fault for not communicating it. I figure that giving everyone the ability to move on when they're ready will help fix the bottleneck problem and cut down on frustration.

I think the next step would be to make it so you can fetch all the exercises, and when you complete an exercise you decide what you want your next exercise to be. Right now there's no progression, it's all just random.

After that we can stop having 'trails' and just detect which exercises exist for a given language.

This change affects: @msgehard, @steveklabnik, @BrianHicks, @rubysolo, @theotherzach, @DarthStrom, @cretan, @seeflanigan, @etrepum, @skmetz, @n1k0, @henrik, @martinsvalin, @bostonaholic, @markijbema, @Trevoke, @tevanoff -- I'd love to hear thoughts if you have them.