Automatic selection of mol v2000 or mol v3000 encoding

[Nitvex]

Is your feature request related to a problem? Please describe.
Introduce a single method to get a molfile from a structure. For now, calling ketcher.getMolfile('v2000') can not be applied for certain features such as enhanced stereochemistry. So you need to call the ketcher.getMolfile('v3000'). With this approach you need to know, which version of molfile is supposed to be used.
It is required to simplify determining versions of molfile and make this process automatic.

Describe the solution you'd like
It is proposed to make version of Molfile parameter optional. Calling ketcher.getMolfile() should return the result for v2000 if possible and if not for v3000.

Note: automatic version selection is already implemented on indigo side. It is required to set molfile-saving-mode: 'auto'.
For more information, refer https://lifescience.opensource.epam.com/indigo/options/input-output-options.html#molfile-saving-mode

[Nitvex]

Files for testing:
Archive.zip

There are two files: v2000 and v3000. You can open one of these files, then call ketcher.getMolfile() and structure is supposed to be saved to corresponding format.

[Nitvex]

For reference. Situations, when v3000 format must be used:

• Structure highlighting – The V3000 format is required for molecule or collection highlighting.
• Enhanced stereochemistry features - The V3000 format is required when using the enhanced stereochemical representations.
• Long fields - If any of the fields with fixed widths for any connection table properties are exceeded, the V3000 format is used.For example, if the number of atoms (or bonds) exceeds 999. This is because the number of atoms (or bonds)on the V2000 counts line can not exceed 3 columns.
• Template block - useful for representing large structures, such as biological molecules.
• New properties supported only in V3000 format - such as atom CLASS and SEQID