Add processor/scheduler/utxo/primitives

Includes the necessary signing functions and the fee amortization logic.

Moves transaction-chaining to utxo/transaction-chaining.

processor/scheduler/utxo/transaction-chaining/README.md

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+# Transaction Chaining Scheduler
+
+A scheduler of transactions for networks premised on the UTXO model which
+support transaction chaining. Transaction chaining refers to the ability to
+obtain an identifier for an output within a transaction not yet signed usable
+to build and sign a transaction spending it.
+
+### Design
+
+The scheduler is designed to achieve fulfillment of all expected payments with
+an `O(1)` delay (regardless of prior scheduler state), `O(log n)` time, and
+`O(n)` computational complexity.
+
+Due to the ability to chain transactions, we can immediately plan/sign dependent
+transactions. For the time/computational complexity, we use a tree to fulfill
+payments. This quickly gives us the ability to make as many outputs as necessary
+(regardless of per-transaction output limits) and only has the latency of
+including a chain of `O(log n)` transactions on-chain. The only computational
+overhead is in creating the transactions which are branches in the tree.