Draft: Feature/reaction side cpds

Objectives of this MR:

• Compute Reaction Specific Side compounds
• Overload the getReactionGraph method to take into account reaction-wise cofactors

Work in progress:

• Optimisation/Architecture
• Unit tests

The side compound identification strategy is up to discussion because to be able to also consider compounds implicated in spurious edges I had to turn the problem upside down: 1: For each reaction, identify the compounds implicated in Main edges as Main compounds 2: Consider all other compounds of this reaction as Side compounds (All compounds - Main compounds)