python3: from __future__ import absolute_import, division, print_function

[ByReaL]

What does this PR do and why is it necessary?

it makes the behavior between python 2 and 3 similar for the below items
from future import absolute_import, division, print_function
it also ensures that changes submitted after this will benefit from this behavior changes

How was it tested? How can it be tested by the reviewer?

travis-ci
visually inspected the divisions in the code

Any background context you want to provide?

division is good it ensures we get same results in both python 2 and 3 but is hard to determine if any existing division 3/2 = 1 will now become =1.5 and brake something
the change is necessary but has a risk.

for example
line_width = wall_thickness / line_count
will work fine because wall_thickness is a float and division will be fine

or here where the code explicit calls for float division by using 2.0
self.get_float("machine_width") / 2.0

and all i could see looked ok, but cannot be 100% sure one division in all the code has not modified it's value.

if there is such case found i could add unit test and fix the problem in that specific instance.

What are the relevant tickets if any?

Screenshots (if appropriate)

Further notes

[foosel]

There were three locations which required integer division (I think ... O_O), see e961234. Rest should be fine though 👍