Cache target table template tuple and its schema in insert executor, to avoid serializing default values on every insert.
Incorporate feedback from Xin and Paul's review comments:
- Make StandAloneTupleStorage allocate and free its own TupleSchema
- Remove StandAloneTupleStorage's cast operator overloads, update clients
- Remove redudant code that Paul spotted in NestLoopIndexExecutor
Merge branch 'master' into ENG-6704-tpcc-perf-regression

Conflicts:
	src/ee/executors/nestloopexecutor.cpp
	src/ee/executors/nestloopindexexecutor.cpp
Merge pull request #1554 from VoltDB/ENG-6704-tpcc-perf-regression

Cache target table template tuple and its schema in insert executor, to ...