This commit refactors the code that handles exporting e-mails opens and
clicks when generating the personal data file to use Doctrine instead of
Paris. I opted to do this in this task as opens and clicks code share
some functionality, and I didn't want to add more code that relies on
Paris, as we are eventually going to remove it.
[MAILPOET-3738]
This commit adds stats about email opens data to the personal data
exported by WP.
To do this, I refactored the code that adds email clicks stats to use
base abstract class with functionality that is shared between both
exporters.
[MAILPOET-3738]
