Fix width (and check functionality) of mapbox search text input

[samuelhwilliams]

When MAPBOX_SEARCH is True, a text box is shown on any map widgets that presumably lets the user search for locations.

The search bar has some width: 50% styling that is taking the width from the window, so is totally broken (see images below): <input style="position: absolute; z-index: 9999; display: block; margin: -42px 0px 0px 10px; width: 50%;" class="pac-target-input" placeholder="Enter a location" autocomplete="off">

We should fix the styling on the search box.

If you pick this up, we should also review the functionality and make sure it actually works full stop.