Time-regularizer / expander to make sure all hours are represented

[oxinabox]

Basically if one has some table which looks like it should have a row for every hour,
but it doesn't.
we want to insert rows with just the time column set and the rest set to missing.

The generalization of this is to also handle it if it is "panel data"
so for each unit being grouped on
it would need to be regularized seperately.
And in that case both the unit and the time column would be filled in