Put frequently used stuff into top-level namespace

[znah]

Typical TF import:

import tensroflow as tf

Typical lucid import:

import lucid.misc.io.showing as show
from lucid.misc.io.loading import load
from lucid.optvis import objectives
from lucid.optvis import render
from lucid.optvis import style
from lucid.optvis.param.random import image_sample

[ludwigschubert]

I just gave this a try and had a hard time finding a reasonable approach. I'd be happy for suggestions!

I agree that the current state is very fragmented and uses more modules than needed, but importing just everything into one top-level namespace also seems excessive. I feel like the biggest win could be to effectively hide the optvis module, but keep the hierarchy around:

• params for all parameterizations
• objectives for all optimization objectives
• transforms for all tranforms
• models for all modelzoo models (?)