Refactoring, support for typing Greek.

Refactored the Word Model/Collection, and how views that depend on this collection are loaded. The reader is still slightly buggy.

Added support for typing Greek on the lessons screen. To make sure your project has this included, run the following commands (after you've pulled from master and committed any changes you have in your working directory):

```
cd /opt/phaidra
rm -rf static/js/lib/typegeek
git rm --cached static/js/lib/typegeek
git submodule add https://github.com/mlent/typegeek.git static/js/lib/typegeek
```

@emilyfranzini @mariamoritz Let me know if this gives you trouble.