Fixed search bar & collapsible legend

[experimatt]

This is the part 2 of @estherrose046's suggestions from the other day. (Part 1 of her suggestions are documented in #189):

• 4. A fixed search bar. It looks just like our current search bar, except it remains fixed at the bottom of that blue 'legend' section instead of scrolling with the sites and only being visible when the "view list of locations" button is clicked.
• 5. we use @amaxama's collapsible legend idea, with the default state being that the blue top legend region is showing. https://tcmap.slack.com/files/U014S9JFV5G/F015FM9QXCZ/file_from_ios.gif
• 6. Optional: Worth thinking about the design of the legend buttons in collapsed view. They seem slightly large to me, could try opacity/some other UI magic
• 7. Optional: The search bar collapses WITH the legend, -or- the search bar always remains visible so that users don't get confused as to why they are only seeing the sites that they searched for. I think I prefer the 'always visible' option...

More detail in the TCMAP Slack thread.

[experimatt]

Mockups for reference

[experimatt]

This may be a duplicate of #99