Request: Add a filter to capability required

[MadtownLems]

In MultiSite, we'd love Network Admins to be able to use Crontrol without exposing it to our standard Site Administrators. Would you consider adding a filter to the required capability so we could change it to manage_network in our environment?

[johnbillion]

I started work on this in #190 but need to finish it off.

[MadtownLems]

oh shoot - my bad. 😣

[johnbillion]

No worries. Sometimes I search for a problem and come across my own issues that I reported months or years earlier and forgot about.