Upgrade to Laravel 5.2

Summary:
Laravel 5.2 has refactored authentication. As the Auth Grove
implements some aspects of the authentication mechanism, this
commit sync'ed our code with upstream changes.

Major changes:

• Configuration has been upgraded
• Routes and HTTP controllers have been reimplemented
• We can now use the AuthenticatesAndRegistersUsers default trait

Minor changes:

• ::class attribute is used instead of a string for types
• /auth route now redirects to /login
• a new auth l10n file handles auth messages in addition to login

Fixes T840.

Test Plan:

• unit tests pass
• manual tests for login, logout, register, reset, recover auth routes

Reviewers: dereckson

Maniphest Tasks: T840

Differential Revision: http://devcentral.nasqueron.org/D412