Drop peer dependency on loopback

The peer dependency was used to control which loopback versions
we are compatible with. Unfortunately it does not work well, e.g.
even when the peer dep allows loopback 2.x, npm installs 1.x version
instead.
Merge pull request #14 from strongloop/feature/drop-loopback-peer-dep

Drop peer dependency on loopback
helpers: Improve ACL asserts

Modify `_it.shouldBeAllowed` to include the actual status code
in the assertion error.

Modify `_it.shouldBeDenied` to assert the exact value of the status
code. Expect the status code configured via `app.get('aclErrorStatus')`,
add a parameter allowing callers to override this value.
helpers: add parameter for request body

Allow tests to send arbitrary request body in the requests being tested.