scalesboard_weight, minor improved dataset and icon
scalesboard_weight_avoirdupois, created new activity

based on the scale engine, this one teaches the avoirdupois mass system
as used in the USA.
Add GCText to handle fonts, add a settings to change current font, change all Text items to GCText
resize the box because for some fonts the height text is bigger than the box (OpenDyslexic fonts for example)