change shell launcher to use main chrome

* Now behaves like original script and AppleScript. 
  <https://www.lessannoyingcrm.com/blog/2010/08/149/create+application+shortcuts+in+google+chrome+on+a+mac>
* No longer needs/creates a symlink to Chrome app.
* Doesn't have PDF plugin loading issue any longer.

fixes https://github.com/lhl/chrome-ssb-osx/issues/8