update select2 - add color markers, limit selection via dropdown

[emillipede]

users have asked for clarity about the species color markers. one short term remedy (since adding meaningful colors to all 250+ species has presented a challenge) is to add the color markers to the select2 drop down (cf https://stackoverflow.com/questions/19789487/customize-a-select-dropdown)

given that mobile users can realistically only select 1 species at a time, I'd also like to switch the select2 back to a drop down (rather than multiple selection pills)

see #211 for other select2 improvements

resolved:
mobile users have asked to filter by species from the toolbar.

rather than display the address search bar, I'd like to offer the "zoom to location" button on the map and, instead of the address bar, display the species filter select2 drop down.

[emillipede]

hey @mrtmrt233 when you test #300 on a mobile phone, is it still a bit weird? on my phone, when I type in the select2 bar, the map and info bars zoom in / go partly off the screen

[mrtmrt233]

yeah that looks like a separate issue

[emillipede]

separate from which issue? the zoom in / re-center is what I had in mind on Thursday @mrtmrt233

[emillipede]

zoom bug fixed - select2 function issue still open