Backport: Cleos/CDT support for various nested types

[vladtr]

• Backport Cleos support for set<optional<T>> and vector<optional<T>> #778
• Backport CDT support for set<optional<T>> and vector<optional<T>> #779
• Backport CDT map support #783
• Backport CDT support for tuple #784

Large Change. Adds feature, changes a number of tests. There is non-kv changes here. I suspect there is an associated CDT change.