Add EPC data to Colouring London

[edwardchalstrey1]

This PR should close colouring-cities#126
However a solution to colouring-cities#250 should be merged first

• Refactor (probably easier in Python) so that we get the following:
  • current_energy_rating is null/blank when "Invalid!" (and then limit the sql column to char(1))
  • floor_level <- check if we can change this to be integer, e.g. substitute ground level for 0
  • wrangle a year out of construction_age_band and make this an int
  • check if UPRN is anywhere in the db already and whether it should be an int
• Update the SQL table with the new data types as per ^
• Write the script that updates the buildings table from the epc table <- what we really want is a way to edit the fields via website API OR at least make sure these are recorded as edits!!! <- see GH issues: Add mechanism to submit bulk edits to Colouring London via automated methods colouring-britain#250 & Data: Energy: Add London/Birmingham energy performance certificate (EPC) data colouring-britain#126
• Make sure the data can be viewed in the correct fields of the app as per PH comment on Data: Energy: Add London/Birmingham energy performance certificate (EPC) data colouring-britain#126
• Add the new doc section to the ETL contents at top of page

[matkoniecz]

what we really want is a way to edit the fields via website API OR at least make sure these are recorded as edits!!!

I have such script and can share it as needed.

In fact I am uploading EPC data for Lboro right now.
If I will get processed EPC/DEC data for London and I can upload also that.