Parse values from doveadm output as integers. Refs #2433

The perl int() function trims whitespaces around the integer token.
Multiply quota with powers of 2. Refs #2433

Avoid trunking the quota size to a decimal value.
Added comments and whitespace to template fragments. Refs #2464
Match "everyone" as user part of mail address. Refs #2464

Without @ the key is matched against the domain part.  See "EMAIL
ADDRESS PATTERNS" in access(5) man page for more infos.