Add ability to run a bulk scan/fix from the admin

[dkotter]

Is your enhancement related to a problem? Please describe.
In #39 a WP-CLI script was added to scan for insecure items and attempt to fix those. This is a nice approach to bulk fix content for sites that may have been converted from insecure to secure but still have references to insecure items.

Not all users will have the access or capability to run a WP-CLI command though, so would be great to add an option in the admin to run the same functionality.

Describe the solution you'd like
Have a place somewhere in the admin where you can initiate a scan for insecure items. Might want some options like the content type to scan and the number of items to scan at a time and maybe an autofix option. This would then run the scan and let you know the items that it finds (and if autofix is on, if the items were able to be fixed).

I can see a similar approach to what is done in ElasticPress, if we want to use that as a reference.