Fix postfix_rewrite_sender_address

Without endif on a new line, alias_database ended up on the same line
as sender_canonical_maps.
Fix relaying mail addressed to local users

The previous configuration doesn't forward mail to local users in all
cases. This adds a virtual alias map that ensures all mails directed
@localhost are forwarded.
Merge pull request #4 from meeee/feature/fix_sender_rewrite_and_local_account_forward

Fix sender rewrite and local account forward