google elevation API backend

[nemesifier]

The code from this view here:
https://github.com/ninuxorg/nodeshot/blob/master/nodeshot/core/nodes/views.py#L258

Could become a generic function which returns an OrderedDict, avoiding to use any django or django-rest-framework API.

The OrderedDict represents a GeoJSON structure (see http://geojson.org).

The initial filesystem layout of the repo could be:

/geojson_elevation/
    __init__.py
    backends/
        __init__.py
        google.py