Add script to recollect data sets affected by refactor

A number of data sets have had their 'dataType' field changed to match
their data type. This means that legacy data needs to be recollected.
Fail process if collect fails
PEP8
Use executable path for pp-collector path

In the one-off recollect script use the path of the executing python
binary to determine where to find pp-collector.
Merge pull request #41 from alphagov/recollect-after-refactor

Add script to recollect data sets affected by refactor