Cleanup, 'cause as @6a68 says, my class names sucked.

* isRequiredEmail=>isEmailImmutable
* requiredEmail=>emailImmutable
* isNotRequiredEmail=>isEmailMutable

Other changes
* Remove the "#back" and "#required_email" CSS, elements with these ids are nowhere to be found in any template.
* Use high level "testElementHasClass" and "testElementNotHasClass" tests instead of low level equivalents.