implement topic points

[jtauber]

In the description I mention earning "Morphologist" and "Septuagint" points. Here's how I think we could easily implement that...

Each Project has a list of topics that are the basis for these points. Each task is tied to a particular subset of these topics. You earn topic points (initially one per item but that can evolve) by doing tasks marked with those topics. We can have project-scoped, per-topic leader boards (once there are multiple tasks with different topics).