Fixed ambiguous auto layout contraints in MainMenu.xib.
Replaced use of -[NSMutableData bytes] with -mutableBytes where appropriate.
Added readwrite property declarations to MIKMutableMIDISystemMessageCommand.
MIKMIDISystemExclusiveCommand is much more fully implemented now, and is usable.
-[MIKMIDICommand description] prints -data instead of -internalData now. Some subclasses (e.g. sysex command) override -data to insert additional data for send.
Added "Send Sysex" button which sends an identity request to MIDI Testbed app. Removed LED test code.