Fixed stray regressions reported by Joseph and Albert

* Label font is not any more erroneously affected by the resizing of the numbox

* The width is now more conservative and accurate

* When a new number was entered that exceeds the numbox width and was replaced by a + or a - and after it was refocused again with a shift pressed (thus entering the append mode), the + did not revert back to the entered number. Now it does (even though you only see the last n digits that fit the numbox--LATER: we may want to add a < or > at the beginning, letting the user know that there are more digits to the left. This however, with the current setup may not be as trivial as it seems, so we will keep it as-is for the time being until users report problems/dislike with the current mode of operation which is still way better than it used to be).