Adjust positioning of bottom map elements

[caseycesari]

Overview

Following up #55, now that the map height is consistent across devices, the position of the map controls along the bottom of the map are adjusted. The controls are positioned so that they are above the footer on the overview map and along the bottom of the map when the sensor pane is open.

The sensor description text is also added here as it was a relatively simple, largely cosmetic change.

Connects #75 Connects #83

Demo

Overview map

Map with sensor pane open

Testing Instructions

• View the site in both a desktop browser and on an iPad, and verify the bottom map controls are also visible.

[alexelash]

@caseycesari

Made adjustments we discussed over Slack in 231443d to move placement of mapbox attributions away from "Back to map" button so that someone doesn't accidentally tap it. Also added a custom compass icon so that it's more visible (ignore weird popup in simulator):

[alexelash]

Checked on an iPad after the changes @caseycesari, LGTM

[caseycesari]

Thanks!