016-pandia

Major changes:

• Replaces the binary merkle tree used for note commitments with a tiered quadtree (#840), which in the future will allow dramatic improvements to the performance of client synchronization (right now we are not yet taking advantage of its fast-forward sync capabilities; this speedup will come in a later update)
• Adds support for IBC channels (#801)
• Adds new commands to pcli for printing information about the chain parameters and summary info (#835)
• Adds an initial custody protocol (#846)