[utils.metric] Rename as measure as some of the values are not real metrics; Add tests for AUC and improve its implementation

[utils.plot] Implement a more fair std.dev. plot using a bivariate gaussian modelling instead of vector addition (thinner regions)

Streamlining

See merge request bob/bob.ip.binseg!12

[script.binseg] Add some utility functions to download URLs to temporary files and save command-lines

[engine.*] Move model summarization to training; Separate static information from dynamic information logging

[engine.trainer] Flush CSV file as we log it (every epoch); Only output minimal information on the screen