Reduce available properties

[IanMayo]

The Meta-Schema includes many properties, for different types of elements.

But, it should be possible to reduce the number, to allow a user to navigate them more quickly.

A core set could include:

• title
• type
• description
• format

Clearly some formats are only applicable to some element types (table for array).

Similarly, some further properties are only applicable to some element types (enum for string).

We may also be able to infer some logical default values (table for array).