Partially cleaned up the APITest.

[odisseus]

• Replaced Arrays.aslist with Collections.singletonList whenever possible, because passing a single array to the former method can be confusing;
• Fixed an error in the recursiveRefs test, where one of the test outcomes wasn't actually checked;
• Suppressed the compiler warnings about:
  • unparameterized generic types, because this test uses the API methods that just return Map without type parameters;
  • unused variables because there is a lot of them, and fixing this right now would require too many changes;
• Replaced assertTrue with more specific assertions for better failure messages;
• Added static imports for assertEquals etc. to reduce the clutter a little bit;
• Added @Ignore annotations to the disabled test cases so that they are visible in the test report.