Add :show command to show animation function

notebooks/tests/Hanoi.mch

notebooks/tests/images/Disc1.gif

notebooks/tests/images/Disc2.gif

notebooks/tests/images/Disc3.gif

notebooks/tests/images/Disc4.gif

notebooks/tests/images/Disc5.gif

notebooks/tests/images/Disc_empty.gif

notebooks/tests/show.ipynb

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

src/main/java/de/prob2/jupyter/commands/ShowCommand.java