The admin page now has the option to send an invite to an email address.
Since there are now two email types (invites and pw resets), the new
sections have been added to config.ini, and email_template and
email_plaintext have been renamed to email_html and email_text
respectively.
Password validation added, configurable under the [password_validation]
section in config.ini. Each criterion is displayed next to the form, in
red or green depending on whether the password passes it. form.html now
looks different because of it, whether it is enabled or disabled. An
error message is now displayed if the user already exists.
