[CB-540] [weinre] easily navigate to spot in DOM

[CB-540] [weinre] easily navigate to spot in DOM

- Web Inspector has a few behaviors here that weinre didn't,
  and so these were added:

  - re-expanding to last selected DOM element on reload
  - expand to DOM element via the inspect() function

- most significant were WiDOMImpl:pushNodeByPathToFrontEnd
  and override in client of DOMNotify:setChildNodes to
  ignore calls made to previously set nodes

- a few drive-by clean ups were done

- added the common/Debug class which adds some nice logging
  methods for weinre developers