CAPX-17 - New Mapping Button

# Ready for review
* Added create new mapping button and help text. 
* Broke out pages into their own file.
* Added button class to links so that they look like a button.
The biggest difference between the two callbacks is: 

if (!$mapper) {
    throw new Exception("Could not load a mapper with provided machine name. Please check url.");
  }

I agree there is some duplicate code between the two callbacks that could be simplified.

There is some upcoming work that will add some additional blocks of content to the page. I find it easier to add this content through the callback function rather that tying it into the form and adding conditionals.