Places/States: Replace "pin" thumbnails with images

[GeorgieBurr]

Replace ”pin” thumbnails on /place/is/state with custom images (EiE will send over these images)
@chrismytton will need to estimate the time this job will take

[emilydrk]

Estimate: 1 day.

[GeorgieBurr]

Seun has sent the images over. We have suggested we can add the images this year.

EiE have requested that they would like to be able to change this data themselves, which begs the image will be stored etc. We can discuss this in the meeting about data, in relation to #174
We have said this work will need to be estimated, and would then take place next year.

[zarino]

Pull request here #245 ready for @chrismytton to take a look at.