Better trust chain output

[mcpherrinm]

Today, we dump all built trust chains.

That could be improved in a few ways:

• Don't print all of them out unless in --verbose
• Warn about un-needed intermediates (but be careful; they may be needed with other trust stores)
• Warn about un-needed roots served in trust chains
• some support for pinning leafs / intermediates

[matthyx]

I would even fail the validation if an intermediate is missing from the presented chain.
Today it validates if the intermediate is present in the CA bundle (which is wrong).