CAS:1271: Cleaning up cas-server-core based on checkstyle rules

Apologies that this is a rather large pull to review but there aren't any substantial changes. I have adjusted the following:

1. Relaxed checkstyle rules our javadocs for unit tests
2. Fixed string concatenation and log messages in areas that made sense
3. Fixed invalid javadoc tags and in areas, wrote new javadoc
4. Removed all trailing whitespace from the code
5. Converted all test cases to use `@Test`
6. Improved checkstyle rules to report more errors
7. Cleaned up files to adhere to the 120-character long line rule, where made sense

It's a large changeset, but most changes are very trivial and easy on the eye to review.