This removes the need for a separate setAction method.
The default action is the empty action, which does nothing. However,
a touch event on a button with the empty action is no longer considered
handled.
Menu::btnContextMenu was changed from a unique_ptr to a plain data
member.
Previously, IconButton instances to be added to button boxes were
allocated with new, but never freed with delete.
unique_ptr makes sure the buttons will be freed along with the button
box that owns them, or when code calls ButtonBox::clear.
The destructor of ButtonBox has been made redundant by this change, so
it's gone.
Setting values are now displayed 10 pixels to the right of setting names, as
passed to MenuSetting::draw.
This commit also contains the following cleanups:
* The height of a row is passed to MenuSetting's draw and touchscreen methods.
* MenuSettingRGBA's magic constant (36) to separate the text for a color's
four components is now a named constant.
* MenuSettingRGBA's color preview squares are now rowHeight - 2 pixels tall,
and have a white border surrounded by a black border to help view the color
it contains in both light and dark themes.
* The rectangle behind the selected setting's name is now drawn by that
setting's drawSelected method.
Originally the font implementation was based on SFont, but it was
recently replaced by an SDL_ttf based implementation, so the name
no longer made sense.
There is no point in precalculating something so cheap to recalculate.
Also, the majority of uses was to compensate for passing the wrong alignment argument.
