Fixes #66

This was a case of pointless css over-specificity.
Fix var clobbering issu, fixes #71

I really wish coffescript had `:=`...
Margin spacing fixes
Fixes #67

This addresses some of the issues with constraint editing and display.
In particular it deals with the issues surrounding existing but falsy
values, such as `0`, and with propagating change events to the right
places, and dealing with resetting the form properly.