Provide generic content structure

[tidyui]

A generic content structure should be provided where the developer can define Content Groups and Content Types that are not directly accessible with an external URL, but can be used as pieces to built other structures. An example of a Content Group could be Products and a Content Type within that group would define what regions and fields a specific product would have. The Content Types should be able to categorize and/or tag if configured on the Content Group.

Each Content Group should appear as it's own main section in left menu with it's own list page together with actions to add, edit, delete and search for items.

Also new Fields and Blocks should be added to reference content of these types from other content or from Pages and Posts

• Base classes
• Attributes
• AttributeBuilder
• Model transformation
• Repositories for EF
• Services
• Manager Views
• Content Picker Modal
• Reference blocks
• Reference fields
• Translation Views