Stimtrack python

[lraiff]

This PR contains three changes:

1. removes metadata and outputs from all jupyter notebooks (the following filter can't act retroactively to already staged notebooks)
2. adds a gitconfig filter that will clean all notebooks of metadata and outputs prior to a commit
3. adds the python and jupyter version of the stimtrack events file

closes #1

[sitek]

Looks good @lraiff ! Could you also remove the now-out-of-date stimtrack files/folder to this PR? Then I think it's good to merge