pulling colors into variables

[mapsam]

This PR adds a thematic color scheme to dropchop (not definite, but was good to work with) and pulls a lot of our shared variables into the _variables.scss file so we can update styles easily without having to skim through a ton of .scss files.

[alukach]

Looks good to me!

[mapsam]

Woop! I also added a couple more fonts, a monospace and a new sans-serif (Roboto). Mostly, I was getting sick of staring at what we had 😉

[alukach]

I do like the aesthetics of this, but one concern that I have with this particular color palette is that it may possibly clash-with/influence the visual styling of data that a user may want to add (assuming #126 and #130 get employed). I think the data and base-layer itself should be the primary focus from a user's perspective (which is something that a really neutral palette supports well).

ie. If I'm processing and styling data that I intend to put on a red-toned site, these colors could make it more difficult to visualize what the styled data will look like when I export it from Dropchop.

[mapsam]

Good point. I'm going to push back a little on this one, just because doing this styling stuff is what's getting me excited right now. Since everything is broken into the _variables.scss file we can make changes quickly. We could even allow the user to switch between bold/light versions.