feature: file enum anonymizer, inject samples in database from a plain text or csv file

[pounard]

TD;DR:

Enum file anonymizer

Given the following plain text file:

none
bad
good
expert

Then:

# db_tools.config.yaml
anonymization:
    default:
        customer:
            level:
                anonymizer: file_enum
                options: {source: ./resources/levels.txt}
  #...

For all the rest, it works exactly like any enum anonymizer, it simply load the file in the getSample() method.

[pounard]

~~Please do not review yet, this will be rebased on top of #225.~~

EDIT: OK it's ready.