Add Java support to RPC API

[atomb]

• Adds RPC methods to support Java verification, including to:
  • load a class
  • assume that a method satisfies a contract
  • verify that a method satisfies a contract
• Adds Python client libraries to support Java verification
• Adds a basic test of Java verification functionality
• Adds support for the Java CLASSPATH environment variable in both saw and saw-remote-api

[pnwamk]

LGTM overall. The few things you and I noted (e.g., fill out TODOs, consider adding a test for the other function) probably worth knocking out before a merge.

[atomb]

I'm in the process of fixing build issues in a separate PR. Once that's merged, I'll rebase this one and hope it works.