Enable DeclarationOrder in Eclipse and IntelliJ

[koppor]

DeclarationOrder should be set in the IntelliJ config - or disabled.

1. Class (static) variables. First the public class variables, then the protected, then package level (no access modifier), and then the private.
2. Instance variables. First the public class variables, then the protected, then package level (no access modifier), and then the private.
3. Constructors
4. Methods

[koppor]

Refs #2765 (comment)
@snisnisniksonah

[tobiasdiez]

Same applies for the rule 'METHOD_DEF' has more than 1 empty lines before. [EmptyLineSeparator].

Moreover, the build should continue even when checkstyle errors are found (so that the unit tests are executed, which are more important then checkstyle issues)

[tobiasdiez]

I found a checkstyle IntellJ plugin, which imports a checkstyle configuration and changes the intellj code style accordingly. I also added a description of how to setup everything in the wiki. So this issue can be closed in my opinion.