Add leaflet drawing for selecting assets

[smcalilly]

Overview

For issue #97. Adds react-leaflet-draw for selecting dynamic polygons and rectangles.

Notes

I had trouble importing the react-leaflet-draw library. It seems to be an incompatibility between the latest version of react-leaflet and react-leaflet-draw. I tried using older versions of both libraries based on info I found in some Github issues but this didn't work for me. So I just imported the EditControl component directly from the library's GitHub and it worked with no problems. Weird!

We have these issues for some more map UX improvements:

• 95

• 96

• 107

• 108

• 109

• 112

Let me know if you have any other ideas for improvements.

Testing Instructions

• Visit https://ccfp-asset-d-react-draw-crf578.herokuapp.com
• Login with the "ccfp-asset-dashboard test user" credentials in the LastPass shared folder.
• Select a project and go to the phases page.
• Select a phase.
• Click "edit assets" in the top left corner.
• Search for some assets.
  • QA the leaflet draw toolbar.
  • Save them.
• Make sure the saved assets load.