* Add documentation for operational node upgrades
* Add documentation for operational node upgrades
* Address review comments
* Some additional detail added after Richards comments
* Restructure page to make more logical sense
* CORDA-986 and CORDA-985 CompositeKey and Signature verification performance fixes (#2467)
* CORDA-696: Create separate transaction types for contract upgrade transactions.
Add rationale around upgrade transactions
Move contract upgrade transaction resolution logic into internal until it's stabilised.
Throw a better exception when contract attachment not found
Default legacy contract constraint to always accepting - needs to be changed to whitelist constraint before merging
Introduce a new upgraded contract interface that allows specifying the legacy constraint.
Remove StateLoader, make all tx resolution functions take in ServicesForResolution
Contract upgrade transactions can handle whitelist by zone constraints
When creating a contract upgrade transaction, make sure the attachment of the old cordapp gets attached when using hash constraints.
Attachment lookup for a given contract class name only scans currently loaded cordapps, and we don't load old versions of cordapps.
CORDA-696: Update upgrade docs
