Improvements related to account registration process using auth_env pluggable module for Hawat.

The account registration process needed more work to get it into stable and usefull state:
* Changed validator for user login from email to string containing restricted set of characters.
* Renamed field 'Login (eppn)' to just 'Login'. It made no sense to be used that was for example with Basic or certificate based authentication service.
* Implemented sendind of confirmation emails after successfull registration to system admins and to the user that performed the registration. The emails are generated using Jinja2 templates.
* Implemented sending of confirmation emails after successfull account activation to the user and as BCC to system admins.
* Added missing rollback() calls to base View implementations to resolve SQLAlchemy errors after unsuccessfull database operation.

(Redmine issue: #3734)