CLOUDIFY-2412, CLOUDIFY-2380 change 'derived_from' in implementation to 'type'
CLOUDIFY-2412, CLOUDIFY-2380 add validation for implementation pointing to non existing nodes
CLOUDIFY-2412, CLOUDIFY-2380 add validation for implementation pointing to non existing nodes
Merge pull request #18 from CloudifySource/feature/CLOUDIFY-2381-impl-review-modifications

Change implementation to specify type instead of derived_from