Switch to Simple Backend

This change implements a switch from the NeDB backend, to the Simple backend, in omega models. The reason for this is that the issues experienced in #42 seem to be related to the database randomly throwing away the character data. (This was not an issue while still on mongodb, and from what I can tell post-mortem, the characters are just missing from the database.)

(To a lesser extent, this might address #56. All testing has failed to exhibit this issue on the new backend.)

Besides those potential improvements for poorly understood issues, it's much faster.

**Note:** Before merging this, [#7](https://github.com/Morgul/omega-models/pull/7) on omega-models needs to be merged in, and a new version published on npm.