Update MKUser.h

[vodaion]

Fix error: Cannot find interface declaration for 'NSObject', superclass of 'MKUser'

[mkrautz]

Hi @vadeara,

Thank you very much for the patch.

The reason the headers don't include Foundation.h is that both MumbleKit and Mumble for iOS have Foundation.h in their precompiled headers list.

Obviously, this doesn't necessarily work for other apps. However, instead of adding Foundation.h headers to all headers in the MumbleKit module, I think that we should encourage a single header for the module, <MumbleKit/MumbleKit.h>. This header includes all the MK*.h headers, but also ensures that Foundation.h and other deps are included before them.

So, I'll NAK this incarnation of the patch. Are you interested in contributing a MumbleKit.h header as described above? If not, I'll do it myself. :-)