Add option to delete revisions every 2 years while cron runs

@proconnor15 do you really need this?

Or maybe you can achieve what you want with the new features in the Drupal 8 module? Take a look here:

https://github.com/adrian-cid/node_revision_delete/issues/15
https://github.com/adrian-cid/node_revision_delete/issues/17

If this solve your problem I will check this as duplicated and once the Drupal 8 module was finish we will port the code to this branch.

For the moment we will stop the new features in the 7.x branch because we are adding new features in the 8.x version and once it will be finish we will add the new features to the 7.x branch.

Thanks for your code and will be great if you can help me in the migration, take a look here:

https://github.com/adrian-cid/node_revision_delete/projects/1

and here:

#2808383: Drupal 8 port?