Feature Request: Allow extra columns in data source for tooltips

type: feature

I have a use case where I would like to create a scatter plot that is color coded by a categorical variable, and include some other text in the tooltip. Currently, I am unable to do this with Chartify because the data frame I pass in has extra columns stripped from it, so they are not available to the tooltip. If you could either not strip those columns out, or add a parameter to the scatter plot function that would allow me to keep a text column, such as label_column it would be very helpful.

Here's an example to illustrate the issue:

I have a dataframe, df, that looks like:

x	y	l	t
1	4	a	'Sunflower'
2	5	b	'Shallow'
3	6	c	'thank you, next'

I would like t column to appear in a tooltip in a scatter plot with the following code:

import pandas as pd
import chartify
from bokeh.models import HoverTool

df = pd.DataFrame({'x': [1, 2, 3], 
    'y': [4, 5, 6], 
    'l': ['a', 'b', 'c'], 
    't': ['Sunflower', 'Shallow', 'thank you, next']})

ch = chartify.Chart(blank_labels=True)
ch.plot.scatter(
        data_frame=df,
        x_column='x',
        y_column='y',
        color_column='l')
hover = HoverTool(tooltips=[
    ("Title", '@t'),
    ("Cluster", "@l"),
])
ch.figure.add_tools(hover)
ch.show()

But what happens is that the tooltip shows "Title: ???, Cluster: a". As far as I can tell, there is no way to pass in a list of text to HoverTool -- it has to be a part of the ColumnDataSource.

It looks like the internals of PlotNumericXY.scatter is filtering out columns here. Is this necessary? Can it be made optional?

spotify / chartify

Feature Request: Allow extra columns in data source for tooltips #61