ENH Implement LGCD with rank1 dictionary

[tomMoral]

It would be nice to implement LGCD for rank1 dictionary in dicodile so it can be easily integrated in alphacsc. I would go with the following steps:

• first add a rank1 parameter in dicodile and update set_D and other communication function that communicate D so that it is retireve in rank1. For this first step, the workers should store a full rank D = uv^T (ie forget about the rank 1 inside the worker by computing D from its rank1 form \sum_k u[k]v[k]^T). Also store the rank1 form as a new attribute uv in each worker.
• Then track all steps that make use of D in the workers and update them to use uv if rank1.
  All these steps should already be implemented in sub functions used in https://github.com/alphacsc/alphacsc/blob/master/alphacsc/utils/coordinate_descent.py as each worker runs an algorithm similar to this one. In particular, I think you need to update the computation of DtD, the reconstruction of X and the _init_beta.

[tomMoral]

This has been implemented in #48. Closing this one.