Introduce to .ket file specification attachment point information for super atoms

[kaluginserg]

Background

In this task - the main area is .ket format upgradation and it's Ketcher implementation.
Connected task: #2467 - support SAP instruction for format mol v2000 by Ketcher (+internal data model and Ketcher behavior)

Solution

• update the specification for .ket file format
  • on the sgroup level we need to store information about attachment points.
  • attachment point id
  • attachment point leaving atom id
  • attachment point additional information
• update .ket serializer in Ketcher (save file)
• update .ket deserializer in Ketcher (open file)

Refs

As an example of the attachment point attributes:
Link to the CTFiles format explanation: http://c4.cabrillo.edu/404/ctfile.pdf (2005)
Section: "Superatom Attachment Point", page 33

Acceptance criteria

1. Ketcher should be able to open mol200 file with sgroup attachment point and then save the struct to .ket format (the "attachmentPoints" instruction should exist in the result file)
2. Ketcher should be able to open .ket file with the "attachmentPoints" instruction and should display attachment point correctly in the contracted sgroup tooltip and also this attachment point should be the used as a connection with other structures.