Bar and Line title and text

[fdion]

Overview

This PR improves titles for bar and for line charts with apply_mean and apply_sort variations. It reflects the correct true observations count or derived observations (due to mean). It also shows the correct aggregation function (count, mean, sum) as is appropriate for the plot.

The other piece of this PR is to add text support to line charts, along with a few basic text attributes for bar and lines:

'textfont_size', 'textfont_color', 'textfont_family', 'textposition', 'texttemplate'

If the above is found to be easy enough to use, the same should be applied to scatter.

Testing

Bar titles

With X only (no Y) and apply_mean:

With X only:

with x and y, no mean or sort:

with x and y with sort:

with x and y with mean and sort:

Line titles

with apply mean and sort:

with sort only:

with mean only:

and finally with no mean and no sort (adding country for line dash to fully target all observations in the right order without group by or sort)

text

The previous gapminder data, line chart with text = continent:

In the above, legend is now redundant. showlegend=False and zooming in provides a great way to quickly see what's happening with GDP by continent in a specific timeframe (also illustrating text attributes):

The same can be applied on bar charts:

Closes

This closes #106 This closes #109