Track position information when splitting arguments

src/main/java/de/prob2/jupyter/CommandUtils.java

src/main/java/de/prob2/jupyter/Parameter.java

src/main/java/de/prob2/jupyter/PositionedString.java

src/main/java/de/prob2/jupyter/SplitArguments.java

src/main/java/de/prob2/jupyter/SplitResult.java