Implements username authentication

It's now possible to login with either username or email
That's necessary to be backward compatible for iChain login

app/views/devise/registrations/edit.html.haml

@@ -27,6 +27,7 @@
             = render 'devise/shared/openid'
 
       = f.inputs name: 'Account' do
+        = f.input :username, required: false, input_html: {autocomplete: "off"}
         = f.input :email, required: false, input_html: {autocomplete: "off"}
         = f.input :password, hint: "(Leave blank if you don't want to change it)", input_html: {autocomplete: 'off'}
         = f.input :password_confirmation, input_html: {autocomplete: 'off'}

app/views/devise/registrations/new.html.haml

@@ -6,6 +6,7 @@
           Sign Up
       .panel-body
         = semantic_form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f|
+          = f.input :username, required: true
           = f.input :email
           = f.input :name, required: true
           = f.input :password

app/views/devise/sessions/new.html.haml

@@ -6,7 +6,7 @@
           Sign In
       .panel-body
         = semantic_form_for(resource, as: resource_name, url: session_path(resource_name)) do |f|
-          = f.input :email
+          = f.input :login
           = f.input :password
           - if devise_mapping.rememberable?
             %p.text-right.small