Group sensors by (generic) asset

[create-issue-branch]

closes #155

[Flix6x]

This PR sets up two new tables to be used for our ongoing migration to a new data model, with corresponding classes GenericAsset and GenericAssetType. It serves to let Sensors be grouped by a GenericAsset.

Assets, Markets and WeatherStations should already have a corresponding Sensor (since database revision a528c3c81506). For each of these, a GenericAsset will be set up, grouping only a single Sensor. Also for any new Sensor (i.e. without a corresponding Asset, Market or WeatherStation), a new GenericAsset will be set up. To group new Sensors under a single GenericAsset, see the upgrade instruction below.

Upgrading

Verify that the current revision is 04f0e2d2924a (head) before checking out this branch:

flexmeasures db current
git fetch
git checkout issue-155-Group_sensors_by_generic_asset

Upgrading without making custom Sensor groups

In case you only have Sensors with a corresponding Asset, Market or WeatherStation, run:

flexmeasures db upgrade
flexmeasures db current

And verify that the current revision is b6d49ed7cceb.

Upgrading while making custom Sensor grouping

In case you have Sensors without a corresponding Asset, Market or WeatherStation, and you wish to group some of these together, upgrade in two separate steps and check the new database tables at each step.
For example, to group Sensors 10, 11 and 12 under a new GenericAsset named "incineration line 1", of a new GenericAssetType named "waste power plant":

flexmeasures db upgrade +1 -x '{"name": "waste power plant"}'
flexmeasures db upgrade +1 -x '{"asset_type_name": "waste power plant", "sensor_ids": [10, 11, 12], "asset_name": "incineration line 1"}'

For more options (such as specifying multiple groups and/or owners), see the revision files 565e092a6c5e and b6d49ed7cceb.

[nhoening]

This looks excellent, great to see you're mastering Alembic this well.

I have a few possible improvements to suggest, mostly small stuff. I'll also push my own addition, so that the new dev-classes can be visualized in our util script.

[nhoening]

I think this also warrants a changelog entry under Infrastructure/Support, on the topic of experimental integration with timely beliefs.