Add Location Field type

[jtrungle]

Hi,
I'm new to elixir and been playing around with Backpex so first of all, great work! The experience with it has been positive.

During my time with it I found myself wishing there was a Location Field type, something like longitude and latitude and have the display as a map. I am aware that the challenge would probably be that each developer would have their own preference on mapping solution. Either way, putting the idea out there!

Thanks again!