Gracefully handle plugins that cause validation errors

[amedina]

In either Transitional mode or Reader mode, when a given plugin causes a validation error, the user will be presented with the option to prevent the plugin from running on AMP pages:

• A new section in the AMP plugin admin screen enabling users to specify which of the installed plugins can be deactivated during amp responses when in transitional or reader mode (plugin suppression)
• Alternatively, the UI to deactivate plugins in AMP responses could be integrated into the plugin list table.
• In Reader Mode, the AMP plugin will automatically remove invalid markup and will notify the user there is an issue with the plugin, and the administrator of the site highlighting the offending markup and plugin (same to be done for Transitional mode and Standard mode).
• Provide assistance when encountering validation errors