2.19.0

 * Add PersistedModel.createChangeStream() (Ritchie Martori)

 * Remove trailing whitespace from jsdoc (Ritchie Martori)

 * Update model.js (Rand McKinney)

 * Downgrade version of loopback-testing (Ritchie Martori)

 * Auto-configure models required by `app.enableAuth` (Miroslav Bajtoš)

 * Add loadBuiltinModels flag to loopback(options) (Miroslav Bajtoš)

 * Add a unit-test for searchDefaultTokenKeys (Miroslav Bajtoš)

 * access-token: add option "searchDefaultTokenKeys" (Owen Brotherwood)

 * Fix the test case (Raymond Feng)

 * Fix code standards issues (Tom Kirkpatrick)

 * Add test case to highlight fatal error when trying to include a scoped relationship through a polymorphic relationship (Tom Kirkpatrick)

 * add callback args for listByPrincipalType to jsdoc comment, pass explicit arguments to callback (Esco Obong)

 * mark utiltiy function as private (Esco Obong)

 * fix linting errors (Esco Obong)

 * fix lint erros (Esco Obong)

 * consolidate Role methods roles, applications, and users into one, add query param to allow for pagination and restricting fields (Esco Obong)

 * fix implementation of Role methods: users,roles, and applications (Esco Obong)
