Added methods to set and get snap points

[anthonie-kramer]

BACKGROUND:

• Snap points are automatically created from representions, which can create too many snap points available for Elements.

DESCRIPTION:

• Adds Set and Get methods to the ElementRepresentation which checks if a developer has specified their own snap points.

TESTING:

• This workflow features a Doors function which is published using snap points at the ends and middle of the door object. Drag it around and see the snapping.
  http://localhost:8080/workflows/818a4543-ce03-4688-bf15-d555407abcdb?view=b09eebe9-9857-4fcf-92e4-e4173e928289

FUTURE WORK:

• There may also be Explore changes required to handle null or empty lists of snap points... but it seems to work just fine.

REQUIRED:

• All changes are up to date in CHANGELOG.md.

COMMENTS:

• Any other notes.

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This change is 

[katehryhorenko]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained