Merge tag '5.0-alpha2' into develop

Version 5.0-alpha2
Add inline assets ability.
Improve the debug informations and add them to proxy output.
Add class ExtendedAssetCollection.
Rebirth of the async.js script.
Eventify the complete asset organisation and rendering.
Remove obsolete empty proxy.php.
Set minimum stability to dev.
Suffix all subscribers with *Subscriber.
Use an event to generate the asset path.
Use the correct event name to organize stylesheets.
Display an html icon to indicate inline and standalone files in BE listing.
Display the assigned layouts in BE listing.
Inject the developer tools code after the base tag.
Fix environments isTablet() and isMobile() detection if overwrite is active.
fixup! Use an event to generate the asset path.
Use events to strip and add the static url.
Remove obsolete method ThemePlusUtils::storeAsset().
fixup! Use events to strip and add the static url.
Load related data container only in BE mode.