Allow other modules to have a say on access control

Sites with complex or customised access requirements may find the need to perform additional access checks before having a replicate action allowed.

For example, on a site with a content workflow, it might be important to be able to restrict the ability to perform replications on content that is in a particular state.
Presently, replicate_ui_access checks that the user has the necessary permissions to perform the replication, but this is not sufficient for the above scenario.

I propose adding a drupal_alter to enable other modules to provide their own additional access checks.