Put setplot functions inside example scripts.

This PR combines the setplot.py file in each example directory with the actual example script (i.e., puts the code from the former into the latter file).  This makes the examples even more self-contained.  I'm planning next to collapse most of the directory structure, putting the example scripts directly under pyclaw/examples/, and just have very descriptive file names and docstrings for each example.

Some more involved examples (like shallow water on the sphere) will continue to have their own directory, at least for now.