Cleaned up RecurrenceNetwork tutorial

[fkuehlein]

committed changes:

• Lorenz-attractor example:
  • included spinup in calculation of timeseries to avoid 0. and 1. values in clustering dimension
  • tried to simplify/cleanup the code not relevant to understand pyunicorn (e.g. timeseries calculation, plots)
  • corrected calculation of GCD
  • Transitivity: cleaned up function for epsilon variation, included progress display
• substituted pylab with matplotlib.pyplot
• removed unnecessary imports
• loops for timeseries calculation now based on python lists instead of numpy arrays for better performance
• substituted latex.codecogs links with inline LaTeX equations
• corrected typos