Nucleic Acid builder and general improvements

[JarrettSJohnson]

Addresses #102 #351

Migrating support from Incentive for the following:

• Nucleic Acid builder in the Builder panel (Jarrett Johnson @JarrettSJohnson)
• fnab command to build nucleic acid chains by sequence (Jarrett Johnson @JarrettSJohnson)
• Improvements to nucleic acid building from native structures (Thomas Stewart @TstewDev)
• highlight attachment points for improved usability (Thomas Holder @speleo3)

Co-authored-by: Jarrett Johnson jarrett.johnson@schrodinger.com
Co-authored-by: Thomas Stewart thomas.stewart@schrodinger.com
Co-authored-by: Thomas Holder thomas@thomas-holder.de

[JarrettSJohnson]

Requesting reviews from co-authors: @TstewDev @speleo3

(There's ofc a lot to be done with general good practices, cleanup--but for now just pulled straight from incentive to make the code difference minimal)

[TstewDev]

I agree with the point that there is a lot to be done here with regard to refactoring and improving readability (looking at you editor.py). However, for now I think this is everything we need to add this feature to open-source. We should file a ticket on the incentive side of things to get this cleaned up and then merge those changes in later on.

[speleo3]

I also agree, first sync with open-source, then refactor.

But before jumping to refactoring: Are there any tests? There are none in this pull request.

[JarrettSJohnson]

I also agree, first sync with open-source, then refactor.

But before jumping to refactoring: Are there any tests? There are none in this pull request.

Removed the incentive requirement. All previous tests (which included 'fnab') for this module were brought over during the pymol-testing migration.