Warn when registering with email containing uppercase characters

Closes #884 and #803

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/src/types/apollo.ts

@@ -0,0 +1,5 @@
+import { GraphQLError } from "graphql/error/GraphQLError";
+
+export class AbsintheGraphQLError extends GraphQLError {
+  readonly field: string | undefined;
+}