Refactoring of BaseCheckTestsSupport and better support for UTs

What was done:

1. Refactoring of BaseCheckTestsSupport class
2. Update for BaseCheckTestSupport to let UTs retrieve check messages from appropriate 'messages.properties' file instead of excess hardcoding. Example:

Now, instead of hardcoded "_15:45: this is the checkMessage_" check messages, we will use in UTs something like this:

    public class ForbidAnnotationTest extends BaseCheckTestSupport {

	private String msg = getCheckMessage(<CHECK_CLASS_NAME>.MSG_KEY);

	@Test
	public void testCase() throws Exception
	{
		DefaultConfiguration checkConfig = createCheckConfig(<CHECK_CLASS_NAME>.class);

		checkConfig.addAttribute(... , ...)

		final String[] expected = {
				buildMesssage(15, 45, "arg1", "arg2"),
                };

		verify(checkConfig, getPath("<INPUT_FILE_PATH>"), expected);
	}
        
        ...

	private String buildMesssage(int lineNumber, int columnNumber, String arg1, String arg2) {
		return lineNumber + ":" + columnNumber + ": " + MessageFormat.format(msg, arg1, arg2);
	}

3 . Provided examples of how to use said BaseCheckTestSupport updates:

  a. [simple example - no params needed in check message](https://github.com/daniilyar/sevntu.checkstyle/blob/eee8ebe797f7501f94ecf235f853a2f04fba856d/sevntu-checks/src/test/java/com/github/sevntu/checkstyle/checks/coding/NestedTernaryCheckTest.java)
  b. [more real-world example - check message has some params](https://github.com/daniilyar/sevntu.checkstyle/blob/eee8ebe797f7501f94ecf235f853a2f04fba856d/sevntu-checks/src/test/java/com/github/sevntu/checkstyle/checks/annotation/ForbidAnnotationTest.java)