Avoiding array_key_exists() warnings

Checking if $data is an array avoids some warnings in the logfile.

  ox.php:1102 array_key_exists() expects parameter 2 to be array, null given (2)
Removed Windows-Line-Endings
Created an extra file for each module. Not completed at the moment.
Email-Syncing added - it is in a very "alpha-state".
Added a comment in README.md
Added ChangeMessage() in all modules.
Implemented DeleteMessage() and MoveMessage() in all modules. In
Calendar + Contacts without any funcitonality.
Implemented DeleteMessage() and MoveMessage() in all modules. In Calendar without any functionality. In Contacts only DeleteMessage() works.
Merge branch 'master' of github.com:virusbrain/z-push-ox
Improved Email-Sync, AS-Version 14

The Email-Sync works:
 * Retrieve Mails
 * Delete Mails
 * Move Mails

Sending emails is not implemented at the moment.
HTML-emails are not synced correctly at the moment.

Added GetSupportedASVersion() to ox.php to announce the
AS-Version 14 instead of 2.5.
Implemented SendMail() and HTML/MIME-Messages in Email-Module

SendMail() sends text/plain Mails just fine. HTML-Mails do not work
at the moment.
Receiving HTML-Mails also should work more or less reliable.
Cleanup
Emails are only synced back until $cutoffdate
Added some basic stuff for sending HTML-Emails

Sending "simple" HTML-Emails works at the moment just fine. But not
all variations works ...
Improved sending HTML Emails

The complete MIME-Message will be send to OX directly now.
Send Mails with the configured defaultSenderAddress from OX.

Now emails are going to be sent with the OX-defaultSenderAddress
in the From-Header.
Mails sent via this backend get a X-Mailer Header with the string
"z-push-ox (Version X.Y)".
Forward- and answer-Flag will be set correct now.
Improved flagging of mails

Flags were removed if a mail is answered twice. This behaviour is
fixed now.
Emails which are marked as deleted will not be synchronized.

The GetMessageList()-Mehtod checks if the Deleted-Flag is set. Is
so the email will not be synchronized.
Changed default code-format

Arrays will be formatted much nicer now, not only in one line.