Add initial (mostly working) datastore

Still a few things left to do:
1) Strip out 'interpolated' datapoints, we'll do this via smoothing
2) Write tests
3) Finish the extrapolating of datapoints
Add more datastore tests

Also: Add 'DataSet.channels' property
Add DataSet.fetch_records(). Rename fetch to fetch_channels

This allows us to pull data in either column or channel oriented formats
depending on the requirements of the data analysis we're doing
Fix fetch_records methon in DataSet

The previous implementation didn't account for the order of the channel
datapoint lists.
Minor refactor (DatalogHeader->DatalogChannel)
Refactor to remove interpolated datapoints table

We'll handle this with smoothing
Add get_channel_min/max function
Add set/get channel smoothing functionality
Re-enable deleting of database at end of datastore tests
Add channel smoothing functionality to dataset
Remove 'ts' from initial datalog creation

This should always be present in the logs and it creates some hoops to
jump through if we don't handle it along with the rest of the channels
Merge branch 'datastore'