A recent commit added the potential buyer to an asset's state based endorsement policy.
That change was problematic because if the transfer fell through, the buyer lost control of the asset,
in that they could no longer update the asset or change the sell price or sell to somebody else.
The asset state based endorsement policy is now based on the seller only, and we document
that additional parties could be added such as a trusted third party (although no
such party exists in test network at this time).
This commit also re-adds some necessary verifications, and make other minor edits and
comments to help users understand the sample.
Signed-off-by: David Enyeart <enyeart@us.ibm.com>
