Add `unique` restriction to every field type

[joneubank]

Resolves: https://github.com/overture-stack/lectern/issues/175

For every field type, add a restriction that every record should have a unique value for that field. This is a boolean property added to the restriction of each field type.

Extra Changes

• Since this was adding validations onto the dictionary schema, this was a good opportunity to add tests for the miscellaneous rules that are being enforced by the dictionary schema
• Renaming the JSON Schema generation script to generateMetaSchema.ts

[joneubank]

NOTE: This is currently not enforced by the js-lectern-client