Run content check plugins via batch or lazy load process

Problem/Motivation

At the moment loading content check page is blocked until all content_check plugins are processed, which could be very annoying for content editors.

Steps to reproduce

Create a content with a lot of external links and than try to open content check page of this content via check tab.

Proposed resolution

Run processing of each content_check plugin after content check page was opened via check tab and update state of plugin in report via some lazy loading solution.

Remaining tasks

User interface changes

API changes

Data model changes