Simplify style classes for buttons and labels in DesktopPadView

.idea/encodings.xml

.../de/tobias/playpad/layout/desktop/pad/DesktopPadView.java

...Wall/src/main/java/de/tobias/playpad/util/NodeWalker.java

...l/src/main/java/de/tobias/playpad/view/pad/PadButton.java

...rc/main/java/de/tobias/playpad/view/pad/PadIndexable.java

...ll/src/main/java/de/tobias/playpad/view/pad/PadLabel.java

...main/java/de/tobias/playpad/view/pad/PadStyleClasses.java