Fixed delete user when 2FA is enabled, implemented delete user for admin panel, and the front-end part for invite user. Secured admin panel behind a configurable token.

These aren't used yet, but will be utilized by the icon caching service
in a subsequent patch.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>

Implemented proper logging, with support for file logging, timestamp and syslog (this last one is untested)

Added SMTP_FROM config to examples and made it mandatory, it doesn't make much sense to not specify the from address.

Improve domain detection, should fix attachment problems. Otherwise, set the `DOMAIN` env variable to the correct domain

Improved configuration and documented options. Implemented option to disable web vault and to disable the use of bitwarden's official icon servers