Add ecobenefit view for single tree

[sireliah]

Right now we present ecobenefits for all trees that have trunk diameter.
In the otm-core we use the simplified_tree_benefits function to get benefits from the ecobenefits service. https://github.com/kodujdlapolski/otm-core/blob/devel/opentreemap/treemap/views/tree.py#L123

The data is provided by the ecobenefits service, here in this view: https://github.com/kodujdlapolski/ecobenefits/blob/master/eco/server.py#L54

We would like to add similar functionality, but for a single tree.

1. User clicks a tree
2. Otm-core sends a POST request with tree_diam (application/json) to ecobenefits service
3. Response is parsed in otm-core and rendered to a template

• The endpoint to be used in the ecobenefits is here: https://github.com/kodujdlapolski/ecobenefits/blob/master/eco/server.py#L48, here's docs in the README: https://github.com/kodujdlapolski/ecobenefits#tree-benefits-endpoint
  Please feel free to modify this view if necessary.
• The otm-core part will require some investigation and reverse engineering, but basically we should be able to keep most of changes in https://github.com/kodujdlapolski/otm-core/blob/devel/opentreemap/treemap/views/tree.py#L123.

The templates for the ecobenefits are here: https://github.com/kodujdlapolski/otm-core/blob/devel/opentreemap/treemap/templates/treemap/partials/eco_benefits.html

The branch that should be the target for this change is the devel branch.
Please feel free to open Pull Request with changes that you think are necessary.
I'll be happy to answer your questions!