Our PropertyGrid currently does not support multiple tabs.
The original MonoDevelop implementation added 1 button per tab to the toolbar,
so the user can switch between them.
However, with just 1 tab, this button is confusing, because when you click it, nothing happens.
Thus, I removed the addition of toolbar buttons for tabs here now.
Once we want to support a PropertyGrid with multiple tabs,
we can re-enable this functionality.
A more elegant implementation for example could be to not add a button for the first tab page,
but when a second (or even more) tab page is inserted, buttons for all of them could be added (probably simply by making them visible).