Fix the variant layout
Merge branch 'master' into dev
Merge branch 'dev' into contao3
Merge branch contao3 of git://github.com/MetaModels/DC_General into contao3
First iteration of refactoring for Contao 3.
Updated README and removed some obsolete files.
First version of panel elements finished.
Filter panel content to omit empty panel sections.
Several bugfixes in panel elements.
New snapshot for others to have a look at the current state.
Several micro fixes.
Rename DcGeneral/Callbacks/Callbacks to DcGeneral/Callbacks/ContaoStyleCallbacks.
Rename DcGeneral/Controller/Controller to DcGeneral/Controller/DefaultController.
Rename DcGeneral/View/View to DcGeneral/View/DefaultView.
Do not use class_alias.

class_alias will not work with composer classmap.
Rename DcGeneral/Data/Interfaces/Collection to DcGeneral/Data/CollectionInterface.
Rename DcGeneral/Data/Collection to DcGeneral/Data/DefaultCollection.
Rename DcGeneral/Callbacks/Interfaces/Callbacks to DcGeneral/Callbacks/CallbacksInterface.
Use CollectionInterface instead of Collection for parameter types.
Rename DcGeneral/Data/Config to DcGeneral/Data/DefaultConfig.
Add missing initialisation to BaseContainer::$arrPanels.