operators. RNA property buttons will automatically fill in the label, min/max,
etc if they are not specified. Operator menu buttons will look up the key
combination in the handlers and add it automatically.
uiDefButR, uiDefIconButR, uiDefIconTextButR
uiDefButO, uiDefIconButO, uiDefIconTextButO
uiDefButO takes a context pointer to do the key lookup, don't really like this..