Add node tests

[mydea]

This PR:

• Adds a message showing the time needed to complete extraction (e.g. Time to complete: 75.23 seconds)
• Reintroduces whitespace cleaning in the .hbs files (While it works without it, there are some warnings and some inconsistent results depending on the OS)
  • Note that the whitespace cleaning works a bit different now: It will preserve line breaks, so that the line numbers in the po files are correct.
  • It will only clean spaces/tabs
  • It also converts windows style line breaks (\r\n --> \n)
• Add basic tests for l10n:extract - as well as an infrastructure we can build upon for more tests - this was inspired by ember-cli-release's tests (fixing #37)

[arm1n]

Tried also on OS X and works fine for me - Merging and closing branch, thanks!