Investigate postcode detection

[schlos]

Expected Behavior

Transifex revealed:
"Your request contains a postcode. Unless it directly relates to the subject of your request, please remove any address as it will appear publicly on the Internet."

How it's detected?
https://drive.google.com/file/d/1otsV1VmUg38qtrDoo_23SdoKLkBsGZLH/view?usp=sharing
Screenshot:
(Code for Croatia access only)

Current Behavior

Possible Solution

Steps to Reproduce (for bugs)

Context

• Alaveteli version:
• Ruby version:

Your Environment

• Browser Name and version:
• Operating System and version (desktop or mobile):

[schlos]

https://github.com/mysociety/alaveteli/search?q=contains_postcode

PR: mysociety@bc2267d

More details:
mysociety#3515 (comment)
https://github.com/mysociety/commonlib/blob/b9a38c92e59338548961cb523dd746092db09b25/rblib/validate.rb#L153