Review imports in manageModels (and maybe topicmodeling.py)

[jeroarenas]

We need to review which libraries are imported. In many cases a lot of libraries are not needed, and importing them: 1) will raise warnings, 2) will take time making execution of the services slow.

Remember this is going to run as a dockerized service, meaning that we should try to accelerate execution as much as possible. For this, we need to import only what is actually needed. This can be done in the main after argument parsing.

[lcalvobartolome]

I have reviewed the imports of both "manageModels.py" and "topicmodeling.py" and made the following changes:

1. modules that are specific to just a unique function are imported within such a function
2. modules in use by several functions are imported within the main method when the service that makes use of them is invoked
3. generic imports are kept at the beginning of the script as some of them are necessary before the definition of the main method.

I leave this issue open to review the imports again at a later point.