Need to disallow direct content object delete

[paulgoleary]

Right now the owner of a content object can directly call kill on the contract. This corrupts the elv-master data model because we need the ContentObjectDeleted event to be thrown from the owning library in order to keep indexes in sync.

However, we can't immediately just disallow any account besides the library to call kill because - for other reasons - we took onlyOwner off of the delete content function in the library.

Long story short, we need to figure out the correct way to auth this.

[elv-preethi]

tested PM/qdel branch contract with qfab_cli library content delete command with following scenarios :

• content and library created by same user -> success
• content created by different user. -> if the some one other than content owner tries to access it, throws error.