Export of RNA presets to IDT notation (standard IDT monomers)

[olganaz]

Background
Users may need to generate IDT notation for modified RNA to be able to order this kind of molecules through IDT web site.
This task dedicated to the export of presets with defined subunits.

Requirements
There could be four types of IDT monomers for export:

1. Standard monomers - nucleotides, which could be exported as [s]<Base>[*]
   where:
   Base - standard unmodified nucleotide base symbol (see table below)
   s - optional symbol of the sugar that makes the nucleotide (see table below). If not specified, standard sugar deoxy-ribose (dR) is implied.
   * - optional indicator of modified phosphate. If specified, indicates that Phosphorothioate (sP) is included into nucleotide, otherwise standard phosphate (P) is implied.
   The last nucleotide is considered to lack phosphate, so * couldn't be the last symbol in the sequence.

Examples
TBD

[AlexeyGirin]

Will be tested in the context of epam/ketcher#4495