Add Janitor class

[pavlis]

This implements a new Janitor python class. This can be used to solve a long standing problem with handling Metadata attributes in a workflow. Attributes can become stale and/or inappropriate for the object containing them. An example is "chan" values left as debris by the bundle function. This class implements generic methods to handle cleaning out such debris.

This initial push should be viewed as a draft from coimments by the group. Colleagues please consider:

1. Is the API complete?
2. Are the names rational? They are kind of cutsey but that also makes them memorable.
3. Read the docstrings and critically evaluate behavior of the methods.

I think the tests may be broken on the very last thing run. I'm pushing this anyway as I'm a bit suspect of my pytest setup and hoping I can get some insight running this on github.