log scanner: adding cli to managing scans.

[sravotto]

This change adds a subcommand to the visus cli to manage scans, allowing users to add/delete/view/test scan configurations in the database.

The configuration is represented in a yaml file, like in the following example:

name: cockroach_log
enabled: true
format: crdb-v2
path: /var/logs/cockroach.log
patterns:
  - name : events
    regex:
    help : number of events

---

This change is 

[sravotto]

closing in favor of #124