Correctly persist slides to local storage

Also just have one presentation representing all slides
Permanently remove models from collection
Edit slides by finding them from the collection
Show existing title if present in the input field
Edit and view presentation links added
Title and content placeholders

Also back button and save message for slide editing
Increment slide number for slide titles when adding new ones
Added grunt CSS plugin
Use class names instead of IDs

Plus semantic tidy up
Basic slide show added
Don't navigate straight to home, include it in the index
Navigate with the arrow keys plus fullscreen option