Add view support

[DarkoKukovec]

Add support for views (similar to sql views) - add a view to the collection that holds a custom list of models

Requirements:

• Has a name in collection (optional)
• Belongs to a collection
• Has a type (model)
• Can have a sort function
• Can force uniquenes
• Has a subset of collection methods
  • remove()
  • removeAll()
  • length
  • list (observable)
  • snapshot/toJSON
  • jsonapi mixin
    • fetch()
    • fetchAll()
    • sync()
• view standalone serialization/deserialization
• view in collection serialization/deserialization
• docs

Creation:

collection.addView(name, {
  type: modelType,
  sort: sortFn, // optional
  unique: true, // optional
});