Make EV comparison relative

As it is now, the EV grid in the EV comparison tab shows the absolute EV of the best action, when what we are really interested in when using this tab is the relative EV.

The EV shown should be: Chosen Action MINUS Compared Action

So if the EV of opening (chosen action) is -2% pot and folding (compared action) is 0%, the EV shown should be -2%.

If we want to see the absolute EV of the best action, we can already do that in the EV and Strategy+EV tabs.