Changed distribution keyword, casted some attributes to float, remove…

[ghost]

This fixes #3783, but there were other issues discovered underneath these fixes.

1. The incoming object to be serialized has the structure self._distribution['distribution']['mean'], self._distribution['distribution']['stdev'] etc, but the write method expects self._distribution['distributionParams']['mean'] (anomaly_likelihood.py line 318-321)

2. The read method did not expect distribution or distributionParams (anomaly_likelihood.py line 274-279) thus when the serialized object was read back into memory it did not have a matching structure.

3. The incoming values cannot be serialized by capnproto because they have the type numpy.float64, so we cast them to float (which is a double) (anomaly_likelihood.py line 318-321)

4. The AnomalyLikelihoodRegion.capnp file uses Float32 (not a double) instead of Float64.

@rhyolight I'm one of the developers working on Grok, we need to use these serialization methods, if you want some time to talk on the phone about these changes I would be happy to do that. There is some confusion here as to how you guys are serializing datetimes, looks like you just save an integer in place of it to preserve order, (why not serialize a timestamp and recreate the datetime object?)
Please do look over this code though, because it throws a fatal KeyError as is. Greatly appreciate all the help given on the forums!

[rhyolight]

The CircleCI build hung, so I restarted it. We received @kyle-sorensen's contributor license and we're processing it. I saw it. This is good to merge.

[rhyolight]

I'm trying to fix the CircleCI build here.

[rhyolight]

Ignore these two validation failures:

• Contributor Validator because I've confirmed he has signed, it just is not processed yet
• continuous-integration/bamboo because we know it is not running on PR, which is ok as long as the other two CI builds pass.