feat(common): improves promise chaining using the `$then` method.

BREAKING CHANGE: `$then` and `$asPromise` callbacks arguments have changed, `$promise` as public property is deprecated.

$then and $asPromise callbacks will now always receive the related resource as first parameter. Last promise result/rejection reason
will be located in the `$last` property of the resource.

Replace references to `$promise` by calls to `$asPromise()`.
docs(): updates docs related to $promise
fix(common): removes promise clearing in `$cancel`
chore(): adds model mixin deprecation notice
refactor(factory): renames $anonymous() to $isNested()

BREAKING CHANGES: Renames $anonymous() to $isNested()
docs(): rephrases reference to anonymous models by nested models
chore(): moves style warning to $send
docs(): some refactoring
1.0.0