Add some grunt scaffolding to run perf tests

Add grunt tasks to do the following:

* Inline a JS file at the end of an HTML file.
* Run an arbitrary shell command on a device (part of the sdb
  task).

Add grunt config to enable performance testing:

* Add a task to inline a JS file which saves performance.timing
  to localStorage.
* Add a task to push a localStorage dump script to the device.
* Add a task to run the localStorage dump script.
* Add a task to reinstall the app, stop/start it 10 times, then
  dump localStorage to the console.