Add possibility to include properties from other models

[sirex]

There are situations, when same set of properties are used in multiple models. Repeating same properties multiple times, makes it difficult to maintain manifest tables.

To fix that, we could add possibility to include properties from other models:

model	property	type	ref
Place			id
	id	integer
	name@lt	string
Town			id
		include	Place
City			id
		include	Place

Here, Town and City includes id and name@lt from Place.

All three models have same set of properties. Properties ar defined in a single place and imported into Town and City models.

base models do not include properties, base is used to define model Entity and semantic meaning, base is also used to assigned same identifiers to different models of the same entity.

Models of the same base might have different set of properties, that is why, we need include type, to explicitly specify, properties, to be added to the model.

Includes could be also possible on top of a property, for example:

model	property	type	ref
Country			id
	id	integer
	name@lt	string
City			id
	id	integer
	name@lt	string
	country	ref include	Country

Where ref include specifies, that City should incluce all Country properties on top of City/country property.

Also, source values should be joined togeter if including on top of a property, for example:

model	property	type	ref	source
Country			id	/cities/country
	id	integer		@id
	name@lt	string		@name
City			id	/cities
	id	integer		@id
	name@lt	string		@name
	country	ref include	Country	country

Example abbove should be interpreted as follows:

model	property	type	ref	source
Country			id	/cities/country
	id	integer		@id
	name@lt	string		@name
City			id	/cities
	id	integer		@id
	name@lt	string		@name
	country	ref	Country	country
	country.id	integer		country/@id
	country.name@lt	string		country/@name

This would work in a similar way as XSD ref references.

Alternative options, how include syntax could look:

1. include is provided in a separate row:

   model	property	type	ref
   City			id
   	country	ref	Country
   	country	include	Country

   Con of this option is that country property name is dublicated, but on the other hand, include is not a property type. include is a macro used to include properties from other model.

   Pro of this option is that this would better allign with include on the model elvel. In this case, only property name needs to be specified, in order to include on top of a property. This gives more consistency.

2. Maybe ref is not needed when include macro is used?

   model	property	type	ref
   City			id
   	country	include	Country

   Similarly as with the first option, ref could be inferred and there is no need to specify it explicityly. On the other hand, we might want to include on top of a backref property, in this case it is better to specify property type explicitly.