Capture "pref_name" from ChEMBL

[jsstevenson]

As of v34

Pref_name curation. Progress has been made towards standardising drug and clinical candidate pref_names (in MOLECULE_DICTIONARY.PREF_NAME) whereby an approved drug name (FDA /EMA) is assigned in the first instance, if available. If not available, the USAN is assigned, followed by the INN name, respectively. If the USAN/INN name assignment is ambiguous, the FDA GSRS preferred name is used. A company research code, or Clinical Trial intervention name, is assigned if no standardised name is available. For virtual parent compounds, progress has been made towards assigning a distinct pref_name (typically based on the FDA GSRS preferred name) that differs from the child compound name.