Add usemin part to gruntfile
Add usemin task to package.json
Refactor the gruntfile and rebuild

Removed the now obsolete sed part and integrated a working solution
for revisioning files
Remove test timestamp replacement part
Restructure gruntfile

Move tasks that require manual interaction to the top
Remove static file handler from dist task

We no longer build assets with each grunt dist run but require a
dedicated dist-assets task. The later will minimize assets and copy
them to the dist folder

For this to work, we need to change the clean task to no longer
wipe the dost directory clean on each grunt build
Rebuild with revisioned files