add ability to set extra params to oauth2 url endpoints

Co-authored-by: Benjamin Sellers <bsellers@gmail.com>
Add StreetLend.com to list of sites using SecureSocial

StreetLend.com http://www.streetlend.com/ is a website I created to help neighbours lend things to each other. It uses SecureSocial for authentication.
Enable retrieving email address from LinkedIn

For this to work, the 'default scope' for the LinkedIn application must be set to something that includes access to the email address. If that is not set, this code doesn't fail but the email address will be set to `None`.
Add OAuth2 provider for LinkedIn
Added strings to securesocial.conf in demos

Added some configuration strings to the demos.

onStartSignUpGoTo=/login
onSignUpGoTo=/login
onStartResetPasswordGoTo=/login
onResetPasswordGoTo=/login

This allows users to know how to make custom login
flows without having to dive into the source code.
explicit scala version
Not needed after all Revert "explicit scala version"

This reverts commit 0d386192f665648335891b3a27d5da93bba8ebd3.
added dutch translation
updated messages and added correct locale
Use play.Application as a type for constructor's argument because this is what is passed
Fix refference to views: should be views.html.custom, not view.custom.html
Implements getNotAuthorizedPage for MyViews
better dutch texts
registeren is the right term
texts improved
Typo in comment
Fixed typo in example config

https://github.com/jaliss/securesocial/issues/284
- upgrade to Play 2.2
Add indication to register event listeners in play.plugins.

It took me a few minutes to figure it out, finally got if from the scala sample code.
Merge pull request #247 from gmethvin/linkedin_oauth2

Add OAuth2 provider for LinkedIn