Make email mandatory + sign in translations

config/locales/en.yml

@@ -68,11 +68,14 @@ en:
         brand: "Brand"
         image: "Image"
         name: "Name"
+      session:
+        email_address: Email address
+        password: Password
       user:
-        username: "Username"
-        email_address: "Email address"
-        lang: "Language"
-        password: "New password"
+        username: Username
+        email_address: Email address
+        lang: Language
+        password: New password
     errors:
       models:
         completion:
@@ -100,6 +103,12 @@ en:
           attributes:
             name:
               blank: The puzzle name cannot be empty
+        user:
+          attributes:
+            email_address:
+              blank: Your email cannot be empty
+            username:
+              blank: Your username cannot be empty
   completions:
     edit:
       title: "Edit completion"
@@ -160,6 +169,7 @@ en:
       edit: "Edit"
       import: CSV Import
       open: Open
+      sign_in: Sign in
       save: Save
     field: Field
     none: No field selected