Add Generic Block rendering

[tidyui]

Add support for rendering "Generic Blocks", i.e where the fields are just rendered using the view components for the fields. This also requires that blocks are exported completely different through the manager Api as blocks does not contain meta-data for fields.

[tidyui]

This should probably consist of two parts. First some way to mark the BlockType that it should be serialized as a generic block, like a GenericBlockAttribute, and secondly a Vue component generic-block that can be registered as the component for the block. This way it would be possible to create custom block components the uses the generic serialization model if desired.

[tidyui]

As support for .NET Core 2.2 ends in December we have to push this feature to 8.1 and focus on migrating to .NET Core 3.0.

[psandgren]

Nice work! Speeds up development a lot!