#537 - extending $cql operation, adding tests, cleanup

[c-schuler]

For review:

• Change "expression" parameter to be optional
• Add "content" parameter
• When both the "expression" and "content" parameters are present return only the expression specified
  • Add tests
• When only the "expression" parameter is present, behavior should not change
  • Old tests should still succeed with updates
• When only the "content" parameter is present, return the results of all library expressions
  • Add tests
• Add updates to both R4 and STU3