Adds new aggregation method choice when resampling the TimelinePlot. Also renames fields for consistency and UX.

Fixes incorrect count of groups due to multi-exclusion query

Renames value_key to agg_value_key for the plot kinds where it is aggregated

Deepcopy fields prior to returning them. This allows code further down the line to modify the fields by reference without leaking global scope references.

Creates a new Django Form subclass modifying its behavior such that the initial value of fields is coalesced when the data attribute does not contain the corresponding field