Rewrite module

Here is a rewrite of this module, which aims to be more generic and follow the logic of the commerce patch #1736850: Adding the checkout redirect feature

What have been done :

• Remove the menu system used to redirect users
• Redirection now happen in a hook_user_login() (expect for registration which happen in a submit function)
• Provide a setting to configure where the user should be redirected login or register form

This new approach should fix following issues too

• #1541616: LoginToboggan Unified
• #1390846: Acces denied after logged and visit checkout/xx/user/register or checkout/xx/user/login

Feel free to test it and give feedback.