Notify user of certificate errors while pushing

Previously, if a server's certificate failed authentication while
connecting for push (if, for example, the certificate had expired), then
the attempt to connect would fail, and another attempt would be tried
later.  After a certain number of failed attempts, no further attempts
would be made.  Meanwhile, the user is oblivious to the failures, and it
could be quite some time before the user realizes that they are not
getting email.  Even when they do realize it, they would not know the
cause.

With this commit, users receive a notification when such failures occur
while connecting for push.  (These notifications are already generated
with failures while polling.)  Tapping the notification will take the user
to the relevant server settings where they can choose to accept the
certificate.
Eliminate the 'if available' connection security options

These options originated in the AOSP email client from which K-9 Mail was
forked.  They provide an odd combination of 2 features:

1. Don't bother to authenticate the server's certificate (applies to both
SSL/TLS and STARTTLS); i.e., blindly accept all certificates.  This is
generally a bad security policy which is susceptible to MITM attacks.

2. If STARTTLS is selected but the server doesn't claim to support
STARTTLS, then proceed without using encryption.  This, too, is a bad
security policy which is susceptible to MITM attacks.

Since the time that K-9 Mail was forked, a couple things have changed:

> K-9 Mail has implemented the ability for users to review and permanently
accept individual certificates that would otherwise fail authentication.
With this ability, there is no need for a user to subject themselves to
the ongoing risks of feature 1. above.  Hence, this commit removes feature
1.

> The AOSP email client has changed its behavior and no longer permits a
security downgrade to an unencrypted connection if the server doesn't
claim to support STARTTLS (i.e., they eliminated feature 2. above). K-9
Mail should do the same.  It's unlikely that a server is going to provide
STARTTLS on an intermittent basis, so providing a contingency for such
unusual behavior is an unnecessary risk.  Hence, this commit removes that
feature as well.

Effect on existing users:

If the old connection security setting was "SSL/TLS (if available)" (which
now gets remapped to "SSL/TLS"), and the server does not provide a
certificate that can be authenticated, then a "Certificate error for
<account name>" notification is generated telling the user to check their
server settings.  Tapping the notification takes the user to the relevant
server settings, where the user can tap "Next" to review the certificate
and choose to permanently accept it.  This process would occur during the
first syncing of folders after application upgrade or (in the case of
SMTP) during the first attempt to send a message.

If the connection security setting was "STARTTLS (if available)" (which
now gets remapped to "STARTTLS"), and the server does not provide a
certificate that can be authenticated, then the same process as above
would occur.

If the old connection security setting was "STARTTLS (if available)", and
the server doesn't claim to support STARTTLS, then the user would get a
certificate error notification which would lead them to the server's
settings.  There they would need to choose a different connection security
-- most likely "NONE".  If they didn't change anything but instead just
tapped "Next", the server settings would be checked again and a dialog
would pop up saying, "Cannot connect to server. (STARTTLS connection
security not available)". (The implementation of notifications when
STARTTLS is not available is not actually included here -- it's in the
commit that follows.)

Regarding the changes to providers.xml:  in cases where the scheme ended
with "+ssl", the schemes were simply updated by appending "+".  In cases
where the scheme ended with "+tls", a check of the server was made to
assure that STARTTLS was available before appending "+" to the scheme.
Domains paran.com and nate.com failed the check and were removed because
no current information could be found.  Domains me.com and mac.com also
failed and were updated based on http://support.apple.com/kb/ht4864.
Provide notification if STARTTLS is not available
Eliminate WebDAV STARTTLS security choice

STARTTLS doesn't really apply to WebDAV and should never have been made
available as an option.

Pre-existing settings will be re-mapped to SSL/TLS.
Restart pushers after editing server settings

If an error occurs while connecting for push (for example, if the server's
certificate fails authentication), several more attempts will be made to
connect, then finally all attempts will cease.

This commit makes it so that pushers are restarted if the user goes in and
edits the server settings (presumably because the user was notified of a
problem and is attempting to fix it).  Without this, the user could fix
the problem and would still not receive email via push.
Show account name in certificate error notifications

getName() shows the user's name from the first identity for the account.

What we really want is getDescription(), which is the account name that
shows in the account list.
Fix the K9mail-errors folder

Error messages were not being put in the folder because of a problem with
how loopCatch was being handled.

It looks like this problem goes back to commit 5aea9e7.

Additional device info has been added to the error messages.

Also, now the feature is only enabled in debug mode.
Use buffered output streams for all output

POP3 already does this.

This is a more general solution to the problem
addressed in commit 8bfd6ca.