Support agents information in SMILES format

[dariasviridova]

Business need:

Reagent - substance that can be added to mixture of reactants to trigger a chain of chemical reactions. Reagent is not consumed during chemical reaction.
Chemical condition specifies the condition under which the reaction shall go (temperature, UV etc.).
Reagent and condition are defined above or under the arrow and are considered as separate reaction participants. In SMILES format specification reagent and conditions are united with entity agent.

1. System shall detect agent(s) from ket as molecule/text that is located above or below an arrow (in the area bounded by perpendiculars passing through the end of the arrow).
2. System shall write agent information in 'Daylight SMILES'/'Extended SMILES' format according to format specification.
   2.1. Agent block shall be written according to spec rules :

Reactions are indicated in SMILES by specifying reactant, agent and product molecule(s) separated by the "greater-than" symbol ('>').
for example:

2.1.1. When agent is presented with text-based agent, SMILES does not support text-elements and text-reagents are lost.

3. System shall communicate "Daylight SMILES"/'Extended SMILES' format to Ketcher.

4. Indigo shall be able to retrieve agents from "Daylight SMILES"/'Extended SMILES' and write them into ket format.