Remove Psydac submodule, change doc style, require pyccel<1.8.0

• Remove psydac submodule
• Require pyccel<1.8.0 to have faster compilation
• Move mass- and basis projection operator docstrings to correct place
• Shorten README
• Shorten LICENSE
• Show notebooks in Tutorial doc (using the package nbsphinx) - this is not working yet because pandoc is missing in the Centos image from MPCDF.
• Increase eps when drawing with "disc" setting (particle imbalance)
• Fix quickstart and uderguide doc
• Fix example orbits tokamak. Fixes #201 (closed)
• Change doc appearance to Python style.