Break out component libraries

[JimCircadian]

Many components of icenet are generalisable for data centric workflows. Many companion projects are relying on this happening in the not too distant future (though they can just use the icenet library in the meantime!)

• Data downloaders split out from library
  • This can drive the decoupling of the EASE2 projection which will be awesome for the downloaders
• Preprocessors split out from library
• To review but not necessarily action - create a plan
  • Training / Prediction harness
  • Plotting from predictions, potentially - certainly looking at automated plotting / visualisation of data stores is a thing

Consider other components around the place, particularly in icenet-etl

[JimCircadian]

Having undertaken the download-toolbox and preprocess-toolbox split for icenet 0.4, as well as looked at the structure within the icenet 0.3 for training and prediction, I've updated the description accordingly. There is possibility for too much to go into this, but might be some interesting harness / plotting movements into other tools that can reside in a more generalised environmental forecasting sense. Worth reviewing w.r.t icenet 0.4 once the work there is concluded.