"Uncompressed XML Files" format variants

[Friedrich W. H. Kossebau]

Hi,

I would propose to remove the option "Uncompressed XML Files" for non-
developer buils, or positively said, only enable it for developer builds.
Reasoning:
* only confuses the user ("what is the difference to compressed?")
* cannot be opened in other ODF programs
* results in data without a mimetype, so badly shown in filemanagers/-dialogs
* no/wrong thumbnails (for content.xml or directory)

Anyone objecting to this? If not, I will finish/prepare a patch and upload for 
review which adds support for uncompressed/directory store formats only in 
developer-like builds. Such a build I assume if NDEBUG is _not_ set. Or any 
better idea what the condition should be?

And while I twist around with that code I would like to change what filename 
is used as id for a document in uncompressed files format, which is currently 
"content.xml". But this id is also used in the window title and in the recent 
documents list so it makes life not easy if there is multiple times just 
"content.xml". I would change the code to use the name of the base dir 
instead.

So okay to prepare a review request?

Cheers
Friedrich