Write a short tutorial starting from a FT data file

[tensionhead]

Even though we still miss quite some functionality (topoplots, interactive artifact rejection), it might be possible to create a little walkthrough starting from a FT dataset mentioned here.

[tensionhead]

Problems at the moment are:

• most FT Tutorials cover topics we don't support: MEG/EEG analysis
• the high-gamme tutorial where we could reproduce the timelock- and time-frequency analysis, is based on edf data which can't be opened with pyedf :(