Feat/improve logs

[ltardivo]

Improves logs through winston.

Two daily-rotated files are created:

• "logs/error-%date.log" (only error message are included) and
• "logs/application-%date.log" (all logs up to BCN_LOG_LEVEL environment variable).

The level is managed via BCN_LOG_LEVEL environment variable (default 2):
0: Error logs only
1: Error and warning logs
2: Error, warning and info logs
3: Error, warning, info and http logs
4: Error, warning, info, http and debug logs

The Console transport can be disabled setting BCN_ENV to 'prod' in the .env file.

[ClemensLey]

Looks good to me