For only web, there is no need to build checkers.
There are so many checkers that will slow down make speed.
Also for some situations, users can build checkers without runners.
Java 7 is now out of support. A large number of people use Java 8.
As the latest Java LTS version, now add support for Java 11.
Due to the policies from Oracle, SunJDK is replaced.
Upgrade judge_client from Python 2 to Python 3.
Add back and support a new judger update method.
Remove the Makefile outside of the folder which not contain any C file.