Local cache

Overview

This branch adds support for a local compound cache, building on work did for generating new compounds from SMILES that was recently modified and added to equilibrator_assets by @elad.noor. A new file, local_cache.py, was added that contains a local_cache class, which provides an interface to the cache. Additionally, generate_compound.py was slightly modified to allow lookup in a local cache.

Examples are given in the local_cache.ipynb, highlighting the various features added.

Key Features

1. A local cache that is derived from the default equilibrator/cache quilt package. The cache is a .sqlite file exported from the quilt package, allowing users to specify local cache locations. The cache can have new compounds added and persists between runs.
2. Functionality to add compounds to the local cache in bulk from a .csv file. By providing an ID, compounds are also registered into the coco namespace for use in reaction text parsing.
3. Functionality to directly query the local cache with a single smiles or a list of smiles to obtain the corresponding Compound objects. New compounds will be added to the local cache.