[#111] Add SpotBugs for Java.

[SiboVG]

This PR fixes #111, replacing the existing FindBugs linter with the updated SpotBugs. It also includes 2 plugins of SpotBugs.

Information:

• Language: Java
• Linter: SpotBugs
• URL: https://github.com/spotbugs/spotbugs

Checklist:

• [x] Only added one linter?
• [x] Is it inside the right language container?
• [x] Is it sorted alphabetically inside the container?
• [x] Does the title follow the template: "Add [LINTER] for [LANGUAGE]."?

For reference, there's some contributing guidelines.