Typo's and QoL changes

[mathiasbosman]

• Typo fixes
• Javadoc url's
• Modifiers should be declared in the correct order
• Try-with resources
• Use constants where possible
• Removed redundant Exception throwing
• Simplified assertions in tests

Some future suggestions:

• Use a codestyle (maybe Google's?) as formatting is a bit all over the place
• Add testcontainer so we can run tests against it (which would enable running them via Github actions)
• Use SL4J for logging
• Use Lombok (@Getter / @Setter / ...)
• Remove serialVersionUID?

(if you want I can take a look at these as well)