Made Adapters Sliceable

[eodole]

I made the adapters sliceable but one concern I have is that when I ask for generic_adapter[0:2] this will return an entirely new adapter instance. Depending on the use case this one matter but could cause problems. I also made a test file but it's not tracked by github, please let me know if I should also upload that.

I also noticed that ElementwiseTransform wasn't being imported so added that as well.

I thought it might also be nice to add the indices of the transforms to the default adapter print, but didn't add that particular feature. I also thought it might be nice to add the feature of appending a new transform via slice assignment so if index == len(adapter.transforms) then simply use the add_transform method.
Resolves #274

[paul-buerkner]

Thank you! I will take a look soon!

[paul-buerkner]

A few short questions:

• Where do you anticipate issues with slicing creating new adapter instances? To me it sounds intuitive that we would create a new adapter instance.
• A test file (if set up in the appropriate test folder etc.) would be great and should be added to this commit I think.
• Index numbers in the printing would be great! How much effort would it be for you to add this?
• I don't fully understand what you mean by "appending a new transform via slice assignment so if index == len(adapter.transforms) then simply use the add_transform method." Can you elaborate? Also perhaps use some example code how what you have in mind would look?

[eodole]

Essentially what i meant with my last comment is that you can add a transform to the end of the adapter by slicing.
I have to find the code responsible currently for printing but I think the modification should be pretty easy

[paul-buerkner]

Ah, I see. Could you show a code example? Let me know once you have added everything you wanted to add to this PR.

[LarsKue]

Appending via slicing is fine, imo. We should have checks in place and error if slices are assigned non-Adapter objects (thus making the adapter self-recursive, each slice is an Adapter itself).

That said, best practice should be to use add_transform (could just call this append as well). We could add an insert method to mimic list behavior, too.

[LarsKue]

Looks good overall, see individual comments for potential changes and discussion.

[paul-buerkner]

@eodole Did you address all the comments by lars already? If yes, can you resolve them? If not, can you make the necessary edits? Let me know if you have questions.

[LarsKue]

I like the changes. I added and modified some parts so that we can fully treat the Adapter like a list now.