Sort out models, data, and tools

0. Re-arrange dirs for cleanliness.
1. Move learned models and data to ~~caffe-mug repo~~ dropbox for now (and a suitable server later).
2. Provide scripts to download models and data as needed.
3. Ignore models and data in the main repo by default. This makes local experimentation convenient.
4. Keep model definitions around.

Orchestrating updates between commits in caffe and uploaded models and data has overhead, but is worth the separation of concerns and keeping the repo lean.