various optimizations, fixes,...

- '.equals()' called on Enum value
- using '==' instead of '.equals()' when comparing references
- java 7: explicit type can be replaced with '<>'
- NodePaint, using AbstractTreeForTreeLayout, codeInspections
- ...
visualizations enum
refactoring, part 1
refactoring, part 2
visual of viselem is refreshed only when it should be