Clean up

[reubenharry]

A longer term issue, with some substeps, mostly for me (Reuben):

• Removing deprecated files: here, I'll defer to @JakobRobnik to identify files which no longer need to be in the repo
• Organization: all imgs+gifs should be in a single img dir, all notebooks (including tutorials) under notebooks, etc
• helper function files in sampler/ should be in a utils subdir
• all tests should be in tests/
• some things like .egg files should be removed and/or gitignored