Added option to not normalize encoders

[bmorcos]

Motivation and context:
Functionality requested in #1191

How has this been tested?
Added a new test

How long should this take to review?

• Quick (less than 40 lines changed or changes are straightforward)

Types of changes:

• New feature (non-breaking change which adds functionality)

Checklist:

• I have read the CONTRIBUTING.rst document.
• N/A I have updated the documentation accordingly. (probably N/A?)
• I have included a changelog entry.
• I have added tests to cover my changes.
• All new and existing tests passed.

Still to do:

[Seanny123]

LGTM.

[jgosmann]

I think normalize_encoders should be added to the Ensemble constructor for consistency. If we are worried about the constructor becoming too long (it is becoming quite long), we should come up with some guide lines which things go in there and which do not.

[bmorcos]

Quick Vote for where to put normalize_encoders?

👍 = put this in __init__
👎 = leave this as a property of the ensemble only

I will make the appropriate changes (if any) tomorrow

[bmorcos]

The people have spoken! (all three of you!)

LGTM

[jgosmann]

I added a commit changing the position of the argument, see the commit message (314171f) for more details. LGTM 🍰