Allow Comment Mail to be active (but not enabled) when StCR is enabled

[raamdev]

The changes that were made in https://github.com/websharks/comment-mail/issues/315 to improve StCR conflict detection made the conflict detection a little too restrictive.

Previously, we could have the Comment Mail and StCR plugins active at the same time, just not enabled at the same time. That allowed a site owner who was thinking of switching from StCR to Comment Mail to install and activate Comment Mail to explore the plugin, without actually enabling it, which is where there could be issues.

As of v161213, you cannot even activate Comment Mail without first disabling StCR, which means if you're using StCR actively on a live site, you have to temporarily stop using it just to explore the plugin.

[raamdev]

Next Release Changelog:

• UX Bug Fix: The previous release made it impossible to activate Comment Mail when the Subscribe to Comments Reloaded (StCR) plugin was active. This release improves upon this behavior by allowing you to activate Comment Mail so that you can review the configuration when migrating from one to the other, and only shows the warning message when you enable Comment Mail. See Issue #328.