Add scenes endpoint (WIP)

[donequis]

This are the issues addressed here:

- Remove call to marketplace from `/mappings` endpoint
        It used to retrieve all the parcels from the estates that
        intersect with the given rect

- Change nw,se params to x1,y1,x2,y2. Names are kept as nw,se for
        `/mappings`, but now can be sw,ne for example.

- Add map `scene cid` <-1:1-> `root cid` in redis

- Add map `root cid` --> [parcels] for pointing valid parcels of a
        scene

- Add a lazy process that generates previous map and flags parcels
    as processed

- Add `/scene` endpoints that accepts a rect and returns the list of
        *valid* scenes for those parcels

- Add a `/parcel_info` endpoint that receives a list of `root cid`
        and returns the mappings for those elements

MISSING:
        - tests
        - redis transactions

[m-sossich]

Issue