Add extension to template file name

Add .ejs extension to template file name in order to enable automatic
file type detection and syntax highlighting.

Signed-off-by: Aleksandr Tsertkov <tsertkov@gmail.com>
Run tests using loopback 2.x.
Fix the code detecting User model

Fix the check to support both `User` model itself and models extending
`User`.
Merge pull request #75 from strongloop/feature/fix-user-model-detection

Fix user model detection + upgrade loopback to 2.x
Merge pull request #66 from tsertkov/feature/add_template_extension

Add extension to template file name
Add configurable authentication header

LoopBackResource was changed from factory to provider to be able to
configure the service.

Add the `setAuthHeader` method to set the custom authentication header.

Signed-off-by: Khashayar Hajian <me@khashayar.me>