Move loop_manager.py module to `managers` package

[Vinicius Arcanjo]

This is a minor code organization to move this module loop_manager.py to managers as recommended in the code organization guidelines that we've been following https://github.com/kytos-ng/kytos-ng.github.io/blob/master/napps/mongodb.md#code-sample

Back then when this feature was delivered we didn't have this guideline yet.