One approach to creating a counter

[ionous]

Fix #137 Rather than ask for all rides from now till festival end; it asks for all rides from festival start and end, then filters and summarizes those. Adds that summary info to the header.

Two downsides:

• the page loads before the event data does, so you see a placeholder "Hundreds of rides so far" first.
• it queries more data in the months of July and August and is already visibly slow. ( maybe we need to do server optimization; and merging the two queries the page does into one. )