Trigger Change Event before Login

Ref #4651

- Manually triggering the change event ensures compatibility with
legacy password managers and browsers not properly firing events on
autofill (which leads to Ember not picking up the entered values).
- Confirmed to fix issues with Firefox <= v30 and Chrome < ~33 (I couldn't really figure out when Chrome started having autofill issues, but it does fix an error around 33, released in March this year).