Show fields based on active query period, with minimum of 1d

[steersbob]

For Graph and Metrics widgets, there are two time selectors: those for the actual values, and those for the available fields. The latter serves to exclude old and inactive fields from polluting the selection tree.

Right now, both are set manually. It would be an improvement if the field time selector is automatically adjusted based on the query period. This makes it more intuitive to view data from previous sessions that may involve history fields that are no longer active.