Reorganise pymica folder structure

[ecasellas]

pymica folder structure is a bit chaotic and should be re-organised as follows:

pymica

• clusters
• io
• methods
  • distance
  • regression
• utils
• pymica.py

clusters may include related scripts to create necessary clusters files.
io may include input and output scripts to adapt input data to pymica class.
methods may include inverse of the distance interpolation and regression modules.
utils may include scripts to calculate distance to sea or ancillary fields
pymica.py is the main Class/script of the package.