message: "ignore"/"unignore" commands: validate user ID
  Extend the accepted patterns so that users are alerted about invalid
  input. These patterns are approximations of the Matrix user ID grammer.
  Resolves
diff: @@ -660,7 +660,7 @@ export const Commands = [
  if (args) {
  const cli = MatrixClientPeg.get();
  - const matches = args.match(/^(\S+)$/);
  + const matches = args.match(/^(@[^:]+:\S+)$/);
  if (matches) {
  const userId = matches[1];
  const ignoredUsers = cli.getIgnoredUsers();
  @@ -690,7 +690,7 @@ export const Commands = [
  if (args) {
  const cli = MatrixClientPeg.get();
  - const matches = args.match(/^(\S+)$/);
  + const matches = args.match(/(^@[^:]+:\S+$)/);
  if (matches) {
  const userId = matches[1];
  const ignoredUsers = cli.getIgnoredUsers();
  