feat!: quantitativeFields is removed entirely from csv and json data specs

[sehilyi]

This removes quantitativeFields entirely from csv and json data specs. This property was unnecessary since we generate scales per visual channel, and the value type (i.e., quantitative vs. nominal) is determined at the time we generate scales, not at the time we parse data. More detailed discussions can be found at #579.

Breaking Updates

If you were using quantitativeFields in the data properties, you just need to remove them from your spec:

data: {
    url: 'https://raw.githubusercontent.com/sehilyi/gemini-datasets/master/data/cytogenetic_band.csv',
    type: 'csv',
    chromosomeField: 'Chr.',
    genomicFields: ['ISCN_start', 'ISCN_stop', 'Basepair_start', 'Basepair_stop'],
-   quantitativeFields: ['Band', 'Density']
},

Fix #579

[manzt]

Great! LGTM.

I know we chatted about this previously, but can you remind me why genome fields are necessary again? Is it something about calculating the "absolute" genomic position? found in previous discussion!

[sehilyi]

I think I need to add a proper description about the genomics fields to our docs.