As the result of things done in CONTEDIT-363, this ticket aims for bundle the Content Editor V2 to Dx-core 6.3 (when it was available)

• Create a new content-editor 1.3.x branch
• Merge migrated code to master of content-editor
• Merge UI changes to ui master
• Merge widgetset-pro changes
• Merge dx-core changes later when Magnolia 6.3 is on development :https://git.magnolia-cms.com/projects/PLATFORM/repos/dx-core/pull-requests/157/overview
• demo - should be merge later when Magnolia 6.3 is on development: https://git.magnolia-cms.com/projects/MODULES/repos/demo-projects/pull-requests/174/overview