Change the way Interactable settings are done

 - Action settings are each in separate objects
 - Option methods always either return the related object or the
   Interactable (never false).
 - Option parameters are expected to be correct. Less type checking is
   done.
Remove Interactable#validateSetting
Rename 'dropzone' in defaultOptions to 'drop'
Per-action snap, restrict, inertia, autoScroll

Currently uses old API.
Better per-action settings
Update snap demo to use per-action API
Add comments for setPerAction
Use per-action API to set restriction in snap demo
Add gridOffset object to default snap options
Merge branch 'master' into per-action-settings

Conflicts:
	interact.js
Use Interaction#action to get per-action options
Fix restriction
Fix autoScroll and inertia resume with resize

Needed to use Interaction#action instead of Interaction#prepared.
Remove actions:[] from snap and inertia options
Enable resize and drag autoScroll in html_svg demo
Fix resize inertia
Enable drag and resize inertia in html_svg demo
Mark Interactable#squareResize as deprecated
Fix resize "square" option
Make a small improvement to per action things