Prototype markup to templates

#### Allow empty eco benefit searches

When the initial page loads and shows all trees we need to calculate the eco benefits for all trees. Previously, empty queries were returning blank results or raising an error if the search query was {}

#### Merge prototype markup into templates

I pulled markup out of the files in /prototype and stitched it into the existing templates.

While the templates are being rebuilt I created an instance_base.html as a DRY place to build content that depends only on the instance.

The eco-benefit search returns markup for both the number of matching trees and the actual benefits, but these two data sets are shown in different places on the template. My solution uses jquery to pull the markup apart and insert it into the appropriate DOM locations.

I did not bring over holder.js because it is a dev-only dependency and adding libraries into our JS build process is non-trivial. I replaced it with a static tree image.

In a future commit the login and registration forms need to be properly subclassed to add additional styling and fields.