Fix non-root level interactions being trained on root level

[MatheusFaria]

Interactions with the level field defined were trained in the root level, which increases the training time. In this PR, I give the option for the user to put the interaction at the root level when:

• it omits the level field
• it defines the level: root

Otherwise, the interaction will belong to another level, and can only be reached through other interactions.

One thing that I wanted to discuss, is the meaning and differences between the level and the context.

[diegodorgam]

Interesting way of tracking the context, kind like a breadcrumb track style. Maybe there is some more ideas to improve this. I'll merge by now, but we should definitely make a call about this feature, there is great potential in this.