GH kinematics in data preparation

[maindlt]

Data preparation: clearly mention (in the documentation and/or in the tutorial notebook 1_data_prep_for_gauss_hermite) that

• care must be taken when implementing data preparation for own data
• the coefficient errors (before applying any systematic errors) have hardcoded minimal values.

The example code in data_prep/generate_kin_input.py

• only works for 4 GH coefficients out of the box, with minor modifications also for 6 GH coefficients
• forces the errors to fulfill vdel≥1, dsig≥1, dh3≥0.005, and dh4≥0.005 (method read_califa(...))
• enforces h5=h6=0 and dh5=dh5=0.3 if there are 6 GH coefficients and the kinematics input is CALIFA or ATLAS3D (method create_kin_input()).