do better redirection from http to https

Redirect using the 'return' directive and the built-in
variable '$request_uri' to avoid any capturing, matching
or evaluation of regular expressions.

It's best practice. See: http://wiki.nginx.org/Pitfalls#Taxing_Rewrites

fixes #241

run status checks asynchronously so that they finish faster, since many checks are waiting on network replies and ought not to block the whole thing

/admin login now issues a user-specific key for future calls (rather than providing the system-wide API key or passing the password on each request)

split management daemon authorization from authentication and use 'doveadm pw' rather than 'doveadm auth test' so that it is decoupled from dovecot's login mechanism

This was done to pave the way for two-factor authentication, but that's still a ways off.

dont save the CSR generated to make self-signed certificates for non-primary domains (it has no value and might be confusing)

Typo

Fix typos in backup status template

Fix typo in mail-guide.html

Sercurity -> Security

catch-all aiases and domain aliases should not require postmaster@ and admin@ aliases because they'll forward anyway

internationalized domain names (DNS, web, CSRs, normalize to Unicode in database, prohibit non-ASCII characters in user account names)

* For non-ASCII domain names, we will keep the Unicode encoding in our users/aliases table. This is nice for the user and also simplifies things like sorting domain names (using Unicode lexicographic order is good, using ASCII lexicogrpahic order on IDNA is confusing).
* Write nsd config, nsd zone files, nginx config, and SSL CSRs with domains in IDNA-encoded ASCII.
* When checking SSL certificates, treat the CN and SANs as IDNA.
* Since Chrome has an interesting feature of converting Unicode to IDNA in <input type="email"> form fields, we'll also forcibly convert IDNA to Unicode in the domain part of email addresses before saving email addresses in the users/aliases tables so that the table is normalized to Unicode.
* Don't allow non-ASCII characters in user account email addresses. Dovecot gets confused when querying the Sqlite database (which we observed even for non-word ASCII characters too, so it may not be related to the character encoding).

see https://discourse.mailinabox.email/t/multiple-domains-in-mail-in-a-box-with-the-domains-being-hosted-elsewhere/56/18

/proc/meminfo reports kibibytes. Lower the minimum memory requirement so that 768 MB (not MiB) also is allowed.

Report the detected memory in MB (not KiB), to be clearer.

Fixes #289.

If bind9 isn't running, dont proceed with other checks because we can't do DNS checks. Even though we skip, add error handling so that a failed call to rndc doesn't crash and that a timeout in a DNS check doesn't crash the status checks.

partialy reverts 93a722f8; closes #287

explain how to add SRV records to DNS zonefile using the API

see https://discourse.mailinabox.email/t/create-srv-record-at-the-dns-server/225

see https://discourse.mailinabox.email/t/postgrey-and-ipv6/227

See https://discourse.mailinabox.email/t/mailserver-limits/228.

see https://discourse.mailinabox.email/t/local-dns-is-not-working-was-unable-to-check-system-status/165/39

admin: ensure multiple concurrent api calls dont confuse the ajax loading indicator (track number of open requets, stop fade animation when it is time to hide)

Fix NS status check - should sort on both ends of the comparison