Update `spharpy.transforms`

[f-brinkmann]

• Docstrings should start with a one liner
• for RotateSH move documentation from __init__ to class docstring and remove __init__ from docs.
• Check if rotation matrixes must be adapted depending on the condon_shortley parameter of the new SH definitions

@mberz again tagging to check if you agree

[mberz]

The class needs to be updated to the new SphericalHarmonicDefinition class, so I'm putting this on hold.