GUI: Fix ListWidget::getEditRect's returned height.
GUI: Fix EditTextWidget::getEditRect's returned height.
GUI: Fix character redrawing behind caret in EditTextWidgets.

This fixes an ugly y position change when the caret is moved to a character in
an edit text widget.
GUI: Fix out-of-bounds check in EditableWidget::drawCaret.

The line "y + editRect.height() + 2" is not included in drawing anymore. Thus
it is allowed to equal EditableWidget::_h.
GUI: Draw caret over the whole height of the edit rect.

This improves the look of the editable widgets.