Minimize title area clutter

[experimatt]

This is part 1 of @estherrose046's suggestions from the other day. (Part 2 of her suggestions are documented in #190):

• 1. We update the header of the legend to say "Twin Cities Mutual Aid Map" instead of "Twin Cities Aid Map"
• 2. We remove some of the padding/space between the legend header and the top item in the legend.
• 3. We remove the "status unknown" filter option, since we have basically eliminated that site category from the map. This and #2 clears up some space to add...

More detail in the TCMAP Slack thread.

[experimatt]

Mockup for reference

[jdalt]

#192