Java target for Ergo

[jeromesimeon]

A possible second code-generation target for the Ergo compiler could be Java/JVM. This could showcase the transpilation capabilities and could serve as an initial prototype for JVM-based ledgers. Work items involved in building a Java target:

• [x] Enable multiple target languages in compiler
• [x] Hook Ergo calculus to Java target from Q*cert
• [x] Port Java runtime for linking and execution of the generated Java code
• [x] Create a template for an end to end test (maybe with an ant Makefile to compile the generated code, pass the input data, etc).
• [ ] Add dateTime support in Java Runtime
• [ ] Testing Java target is consistent with JS target

[jeromesimeon]

Java runtime and testing for Java target added in #457