Refactored operators. (#532)

[ed728]

What this patch does to fix the issue.

Moves operators.py to base/operators.py and creates an __init__.py for the directory. In later PRs Operators will be gradually split into files.

Link to any relevant issues or pull requests.

This is the first is based on a previous PR(#642). That one is too large so it has been split, this is the first part. The other parts are mostly ready and will be made into PRs as soon as this one is done.

The next commits start factoring operators. The next are the branches below:
https://github.com/ed728/blueoil/tree/ops3
https://github.com/ed728/blueoil/tree/ops4
These will be made into PRs when this one has been merged.

Testing.

Manual and CI. Mainly to make sure imports in all modules don't break. Some Arm-related issues did come up but seems to be fine now.

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[iizukak]

@yd8534976
This PR try to solve your issue #532.
Can you check this PR is correct way to solve #532 ?

[iizukak]

Ownership Approval

[yd8534976]

LGTM. Could you resolve conflicts? @ed728

[tsawada]

https://www.python.org/dev/peps/pep-0008/#id19

The preferred way of wrapping long lines is by using Python's implied line continuation inside parentheses, brackets and braces. Long lines can be broken over multiple lines by wrapping expressions in parentheses. These should be used in preference to using a backslash for line continuation.

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