Allow to specify user and accessToken models

Add an options param to `lt.beforeEach.withApp()`, allow to specify
the user model and/or accessToken model that will be used in the
tests.

Signed-off-by: Clark Wang <clark.wangs@gmail.com>
Merge branch 'fix/built-in-models-not-found'
remove unnecessary dependency on loopback

change repository url for this clone.