Implements new admin menu structure #304

close #305
Add Users link in drop down menu
Implements username authentication
It's now possible to login with either username or email
That's necessary to be backward compatible for iChain login
Implements iChain authentication
Merge pull request #528 from ChrisBr/devise

Implements iChain authentication
Set the ichain base url
Update rails/sprockets to fix CVE-2014-7818/CVE-2014-7819
Include disabled omniauth in ichain config for delayed jobs
Use the correct URL for the ichain login
It's always hard to remove another layer of indirection...
Adds disabled flag to user and checks it if iChain is enabled
Implements placeholder for login forms
Merge pull request #529 from ChrisBr/devise

Adds disabled flag to user and checks it if iChain is enabled
Also destroy the ichain session for deisabled users
Do not require answers if it is a yes or no question.
Fix proposal error message. Username -> name.
add username to deleted_user in seeds
add is_disabled attribute for deleted user
remove leftovers from event attachment removal
Provide a helper to point to sign up/in for different configs