Refactor darfix

Refactor the project:

• All the algorithms are called from the dataset. Dataset objects have the control of all the operations of the data.
• A new class Data is created. It inherits from numpy.ndarray and has its own control of the reshaping of the images, and links urls and metadata to each of the arrays.
• The data can be saved into memory or accessed from disk. All modification of the data returns a new dataset with the new data.

Close #15 (closed)