`MyProjectionChanged` events

[dmdashenkov]

With the power of code generation, we can and should generate type-safe events for entity state updates. For example for a MyProjection, we would generate MyProjectionCreated, MyProjectionChanged, MyProjectionArchived, MyProjectionDeleted.

This applies to all entities to which users may subscribe, i.e. entities with (entity).visibility = SUBSCRIBE | FULL.