Fill out new HTML form for location entry

[jywarren]

Followup to #1035, @mridulnagpal asked for next steps. We now have a blank HTML template:

https://github.com/publiclab/plots2/blob/master/app/views/locations/form.html.erb

Now we need to add HTML markup for the location form itself, building from this image:

And using elements from https://getbootstrap.com/components/

We can leave the map as a grey square at the top, for now!

[mridulnagpal]

@jywarren I did not get the exact template could you tell me more about it?

[jywarren]

I think we're hoping to get a set of text and inputs to simply display as best as you can what's shown in the gif (by @ebarry) but that don't need to function just yet. Then we'll do a followup task of starting to plug in functions. Make sense?