Add common boilerplate to getMessageBodyText()'s result

[GoogleCodeExporter]

Currently, this is - if any at all - added by the data store. Instead use 
this text (from synckolab):

{{{
This is a Kolab Groupware object.
To view this object you will need an email client that can understand the 
Kolab Groupware format.
For a list of such email clients please visit
http://www.kolab.org/kolab2-clients.html

---
<<<getMessageBodyText goes here>>

---

Notice:
The information above is only valid, if all clients update this message. 
(ie. a client that updates the attachment but not the message, may cause a 
mismatch)
}}}

Original issue reported on code.google.com by david.black.co.at@gmail.com on 2 Apr 2010 at 10:08

[GoogleCodeExporter]

The Thunderbird extension Sync Kolab seems not to update the body text.

Original comment by keinstei...@gmail.com on 1 Jan 2011 at 7:30

[GoogleCodeExporter]

Why do we need this "stupid" body text? The relevant sync information is in 
kolab.xml

And why should we care to keep body text and xml in sync? Storing data on two 
different places is not only more more, but confusing if its not updated by 
some programs.

Kontact for example doesnt write information about the content of the xml file 
in the body, it only writes:

This is a Kolab Groupware object.
To view this object you will need an email client that can understand the Kolab 
Groupware format.
For a list of such email clients please visit
http://www.kolab.org/kolab2-clients.html

Original comment by STrille...@googlemail.com on 10 Jan 2011 at 10:31