if there are no admins when trying to access the control panel, tell the user how to make an admin from SSH

see #140, #155, df20d447

fixes #158

Conflicts:
	setup/start.sh (changes are in questions.sh now)

Conflicts:
	setup/start.sh (change was already applied)

bootstrap.sh: allow overring the tag to checkout by setting the TAG environment variable (helpful for debugging)

broken by b30d7ad8 when the API began to list both real users and archived mailboxes in the JSON response

when deleting my old /usr/local/bin/mailinabox-exchange-autodiscover.php file from existing systems, don't emit an error if the file doesn't exist (added -f)

replace '-t 0' test with an environment variable since '-t 0' is false when standard input has been redirected and doesn't tell us whether or not we can use dialog for input, but Vagrant must be non-interactive

The secret key that encrypts the backups should not be world readable.

Works like this:

```curl -d "" --user email:password https://.../admin/dns/set/qname/rtype/value```

where the rtype and value default to "A" and the remote IP address of the request, so that a simple, empty POST to

```https://.../admin/dns/set/desktop.mydomain.com```

will point desktop.mydomain.com to the caller's IPv4 address.

closes #140

Move this into system.sh rather than anagement.sh.

This reverts commit eab28c97.

https://github.com/mail-in-a-box/mailinabox/pull/150#issuecomment-53120156

Read timezone from /etc/timezone.

Typo in introduction "later later"

Added dialogs, so that the setup.sh can ask the user any questions even when its piped; Added additional email valdidation for the last step