[boot.js] fix the order problem (issue #578)
Several cleanups in polymer lib and compiler
 - remove ScopedCss class (not needed after we removed the css mangling).
 - remove 'Hashable'
 - delete code that was moved to the 'codegen' and 'observe' packages, and switch
  to those packages instead.
remove bad pub dependency
tiny tweaks
dwc: locking down members that likely should not be accessible from other libs