Catch duplicate authorities in authorities.csv

[adrianshort]

Tests should fail if there is a duplicate authority name.

Not sure about duplicate authority URLs. Do any authorities share the same planning website?

[adrianshort]

96ac906

[dhilton]

South hams and West devon is the only one I've found: http://apps.southhams.gov.uk/PlanningSearchMVC/

[dhilton]

With the local authorities it would be useful to reuse the UK Registers ID for the authority as a unique ID as you can then relate that to a url / boundary ish. The fun bit as mentioned elsewhere are the National parks and the other odd Planning authorities. Yet the Local Authorities covers the majority I would guess.