Extend unindex to support UIDs

[Enet4]

Dicoogle 3 supports unindexing files in bulk by specifying DICOM-level unique identifiers (SOPInstanceUID, SeriesInstanceUID, StudyInstanceUID) instead of URIs. (bioinformatics-ua/dicoogle#391)

The unindex method may then be extended to support this. One possible additional signature:

type EntryKey = "uri" | "SOPInstanceUID" | "SeriesInstanceUID" | "StudyInstanceUID";

unindex(key: EntryKey, entries: Array<string>, callback?): Promise<...>;

Example of use:

await dicoogle.unindex('StudyInstanceUID', ['1.1.1.6666', '1.6.4.4.3231.753653']);