make hook.php show even if the method doesn't exist.

verified no errors if hook.php does not exist.
Add in Sign into twitter image.

@TODO make this look nicer
need some t() with that?
Merge branch 'hotfix/feature/concrete5.org-oauth/img' of github.com:Mnkras/concrete5-5.7.0 into Mnkras-hotfix/feature/concrete5.org-oauth/img

Conflicts:
	web/concrete/authentication/twitter/hook.php
Merge branch 'Mnkras-hotfix/feature/concrete5.org-oauth/img' into feature/concrete5.org-oauth