Replaced drawing background methods, added paper method
Added degrees unit option to polar coordinate system
Added units option to polar-drawing
Add arbitrary properties to drawing elements

eliminated id methods, use new properties feature instead
Removed id property from to-string
Addded distance function to coordinae-system
Added element-type method to Element
Eliminated Element is-text? method
Removed is-text method from Rectangle
Added sqr function to utilities
Added closest method to Drawing
Adds object selection methods to drawing
Fixed attributes typo bug
Adds remove method to drawing
Added envelope adjustment mockup