Improve Email Validation and handling in Mantis

Handle email validation and parsing consistently across mantis, by utilising the HTML 5 Standard.

Fixes the following Issues:

0017275: email matching within Mantis should follow html5 standard
0017276: Allow the ability to block specific domains from registering users within Mantis
0017279: Handling of email addresses within Mantis is not consistent
0017280: Email address validation function strips characters

Follow Up work to Consider:

0017277: Allow use of wildcards when limiting email domain names
0017278: Allow ability to block email domains via wildcard

In addition, we should consider whether to add the html to define an 'email pattern' on the email address registration field so that we can utilise browser verification of the email address.
Or would this currently require a change in the current DOCTYPE we set