Issue 332: Upgrade to Junit 5, hamcrest 2.2

[kmanning]

• Issue Testing: Upgrade to Junit 5 #332
• Replace Junit 4 with Junit 5.7
  • JUnit no longer supports assertThat for third-party libraries, so convert org.junit.Assert.assertThat to org.hamcrest.MatcherAssert.assertThat when hamcrest matchers are being used
  • Push towards using hamcrest matchers in general, over JUnit assertions.
  • @Nested in Junit 5 allows us to drop the hierarchicalcontextrunner dependency. Be sure to apply it consistently going forward.
• Upgrade hamcrest from 1.3 to 2.2
  • Junit 4 pulled in hamcrest dependencies, and Junit 5 no longer does this. Swtich from hamcrest library to hamcrest dependency - this fixes the java.lang.NoSuchMethodError: org/hamcrest/Matcher.describeMismatch errors).