Add integration-test plugin and tests for new supported version formats

To my understanding, integration tests differ from unit tests in that they depend on external state (databases, servers, etc.), I/O, and/or mockups to verify a test, whereas unit tests can be isolated as a POJO (plain-old Java object) and verified as if it were a 'pure' function.  Integration tests are therefore relatively slower than unit tests, and it is desirable to separate the two.

This plugin adds an integration sourceSet that is not called when running `build` but instead is manually executed by running `integrationTest`.

The included tests test various supported version formats that Abrar recently added support for in 400b0666e8c1f5a99f8bd35a7f29b0a38958b84a.  They are classified as integration tests because they depend on external state from a web server, namely a JSON file from the forge maven.