Rework restroom-list view to be mobile responsive

[tymc7]

Context

• Fixes List View has text overlap on small screens #480
• Reworks the .restroom-list module to be its own module

Summary of Changes

• Moves all .restroom-list code (including @media queries) to own file
• Updated .restroom-list class to be a mobile first by changing all class updates to build on mobile rather than break down from mobile.
• Fixed issue in _screen_sizes.scss to utilize variable listed
• Updated #list to be a ul element to be more semantic
• Dropped size of icons in search view because they were too large
• Updated size of toilet icon to be more consistent across devices in the .restroom-list view

Checklist

• Tested Mobile Responsiveness
• Added Unit Tests (Wasn't sure if I should because it's all visual updates)
• CI Passes
• Deploys to Heroku on test Correctly (Maintainers will handle)
• Added Documentation (Service and Code when required)

Screenshots

Before

After

[DeeDeeG]

This looks really cool, thanks!

I'm going to get it loaded on my machine and try it out.

[DeeDeeG]

One little difference this makes (beside fixing #480) is that is can make the restroom icon rather small in some cases:

I think it looks fine, and it definitely helps make good use of the screen width without anything overlapping like it used to. I'm in favor, overall.

I love that this is fully responsive, and that the icon takes up just enough space now. And obviously the overlap issue is gone. Also, thank you for making the HTML more semantic by using <ul> and <li> together. 👍

[DeeDeeG]

Another minor change is that it makes margins around the form about 10 or 20 pixels wider on the "Submit a New Restroom" page, but again it looks fine to me.

[DeeDeeG]

For reasons totally unrelated to this PR, the Travis CI run failed. (It was a network error between Travis and the Gem server, apparently.)

I'm re-starting the Travis CI build -- presumably it will pass this time.

Edit: It passed.

[DeeDeeG]

I approve.

Any other opinions, @mi-wood, @tkwidmer, everybody?

[DeeDeeG]

Will merge soon if there are no objections. 👍