[Ticket/12696] Add events to ucp_register.html



Add events to UCP Register template:

ucp_register_before - add before start of registration form fields
ucp_register_after - add after end of registration form fileds
ucp_register_passowrd_after - add event after passowrd field
ucp_register_language_before - add event before language selector
ucp_register_profiles_before - add event just before begining of registration profile informatiom

All events are inside the registration form fieldset.
All events are inside the registration form

Justification:

Add abbility of extension author to include custom checks or fields inside the registration form. Like age check field/verification.

PHPBB3-12696
ucp_register_credentials_before