feat(admin): add user role dialog

Admins change a user's role and see the change log. The last admin
gets a clear error when deleting their own account.

public/i18n/en.json

@@ -166,7 +166,8 @@
       "DONE": "Your account is deleted.",
       "WRONG_PASSWORD": "The password is wrong.",
       "TOO_MANY": "Too many wrong passwords. Please try again in {{minutes}} minutes.",
-      "ERROR": "The account could not be deleted. Please try again later."
+      "ERROR": "The account could not be deleted. Please try again later.",
+      "LAST_ADMIN": "You are the last admin. Make another user admin first."
     },
     "PROFILE_TILES_HINT": "Choose what your profile shows, and where: open your profile and click \"Customize\".",
     "FAVORITE_PLATFORM": "Favorite platform",
@@ -647,7 +648,18 @@
     "PASSWORD_RESET_TEXT": "The user gets a mail with a link to choose a new password (valid 1 hour). You never see the password.",
     "DONE_PASSWORD_RESET": "Reset mail sent.",
     "ERROR_NOT_PENDING": "This registration is decided already.",
-    "ERROR_TARGET_IS_PENDING": "Accept or deny the registration first."
+    "ERROR_TARGET_IS_PENDING": "Accept or deny the registration first.",
+    "ROLES": "Roles",
+    "ROLES_TITLE": "Roles of {{email}}",
+    "ROLES_TEXT": "The change works within about 30 seconds. The user may need to reload the page.",
+    "SAVE_ROLE": "Save",
+    "DONE_ROLE": "Role saved.",
+    "ROLE_HISTORY": "Changes",
+    "ROLE_HISTORY_EMPTY": "No role changes yet.",
+    "ROLE_HISTORY_ERROR": "The changes could not be loaded.",
+    "ERROR_ROLE_CHANGED": "The role changed in the meantime. The list is loaded again.",
+    "ERROR_ACTOR_NOT_ADMIN": "You are no admin any more.",
+    "ERROR_TARGET_IS_BLOCKED": "Unblock the user first."
   },
   "CORRECTION": {
     "OPEN": "Correct data",