map size is saved between page changes

[trosborn]

This is a fix for issue #612. I couldn't figure out how to write a test for this because AFAIK the button to trigger map size is not loaded in the test environment.

I used session storage which will save the map size within the current tab. If we want it to be persistent, I can easily switch it to local storage.

[anselmbradford]

@trosborn Thanks so much for tackling another issue! I modified your code a little in https://github.com/codeforamerica/ohana-web-search/tree/612-map-size-setting, let me know what you think? You can push those changes or I can open a PR from that branch. I think it would be preferable to add a "click" method to the MapSizeControl API so that it can be programmatically clicked without referencing the DOM a second time. Then afterward check the map size in the sessionStorage just after the map renders. I lumped this code into _pluginsLoaded to eliminate the method that would be called only once.

This could perhaps be refactored a bit more to set the map size before the map renders, instead of just after, but FYI that I have in mind to refactor the map overall to simplify it so that instead of small/large states it's show/hide states, with the only showing state being the large map. This is based on user research feedback.

[trosborn]

Those changes make a lot of sense. Thanks for cleaning up my code! I think it is easiest if you just make a new PR from your modifications.

Since you're planning a refactor of the maps I'll avoid working on anything maps-related for the time being.