fuzzyKcatMatching: refactoring of BRENDA-based approach

[edkerk]

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Description of the new feature:

Instead of having GECKO's fuzzy matching approach directly modify the stoichiometric coefficients in the model, let it populate the model.kcat structure introduced in #156.

• [ ] Use the model.ec.kcat structure as input for matchKcats, instead of the output from getEnzymeCodes
• [ ] Instead of matchKcats always doing fuzzy matching, also have an option to only report (near-)precise matches.
• [ ] Do not have readKcatData to directly modify the stoichiometric coefficients, but instead write k_cat values into the model.ec.kcat structure. Instead, applyKcatConstraints can modify the S-matrix for selected reactions (with updateRxns flag).