Recommend suffixes and mimetype

I believe it is highly unlikely that such suffixes as:
	".owx"
and
	".ofn"
will ever be used, much less dominantly used. Current practice (from  
the OWL API and P4) is to use .owl for pretty much all syntaxes and do  
sniffing to determine the right one.

I have some tendency to use ".xml" for OWL/XML to get it to  
doubleclick into oXygen.

Given these facts, I think we should normalize on ".owl" as acceptable  
for all syntaxes with ".xml" and ".txt" being reasonable alternatives  
for the xml and text formats (respectively).

It does mean that you can't have all the syntaxes in distinct files in  
the same directory, which is a wart. But that really seems to be a  
very rare case (I've never seen it).

IOW, it seems like the syntax specific type tags are a dead letter and  
we should adjust to that reality. I don't see any sufficient benefit  
to switching to them.

Cheers,
Bijan.