Add DataPoints.getTSUIDs() to fetch a list of TSUIDs for each time series
in a span group. Can be displayed in the /api/query output.

Signed-off-by: Chris Larsen <clarsen@euphoriaaudio.com>
Add "show_tsuids" parameter to /api/query to output the TSUIDs with the data
points when the user requests it.

Signed-off-by: Chris Larsen <clarsen@euphoriaaudio.com>