JBIDE-16375: Better separation of Early-access option

* Dedicated preference
* Dedicated section in Software/update page
JBIDE-16375: Uninstall when disabling Early-Access

+ Improve responsiveness
JBIDE-16375: Improve disabling Early-Access experience

* Instead of uninstalling, show an information pop-up about current
"hybrid" state
* Remove site referenced by Early-Access connectors so updates won't
reinstall them later
JBIDE-16375: suggeestion for more clear text for Early Access