Frequency Map (1/2): Query database for frequency slot map

[ljgray]

Query the database for the frequency map that was active when a dataset was collected. Lookup is done by dataset_id, so older datasets which do not have a dataset_id will just use the default mapping that we assume was active at the time.

Changes:

1. Add a task to query the database for the frequency map corresponding to a dataset_id.
2. Add a container type to hold a single frequency map. This does not modify the existing FrequencyMap container for backwards compatibility.
3. Modify the MaskDecorrelatedCylinder task to use the new container
4. Modify the daily config to use the new task(s)

Requires chime-experiment/ch_util#50