Fix logging, add tensorboard support

This MR introduces the following changes:

• adding functions to client.sh and server.sh to be edited by the user to load appropriate modules and source Melissa environment script;
• removing the StructuredLog in favour of classical and centralised log. There is thus one log for all melissa related modules. The log file is by default melissa.log. Duplicates between melissa.log and <scheduler>.0.err are also avoided;
• introducing TensorBoard to the logging of the deep learning training.

Related to #2 (closed)