bug fixes & improvements to ipynb2tex.py and added a template for a cover page.

ipynb2tex.py bugfixes and minor updates:
- all headings moved up one notch: heading# is now chapter, etc.
- catch unicode symbols and convert to ascii
- removed newline at and of single line verbatims
- catch and correctly process empty cells.
- default size inline pngs if no float specs are given (0.9\textwidth)
- \begin{document} now written by the template header.

Added an example cover page for LaTeX workpackage, as an example of custom cover pages.
- docclass for workpackage is provided (add your own logo!)
- header to go with this template: header-wp.tex

example notebook updated to reflect the above changes.