Add ability to add source to charts

[kilemensi]

Description

In order for a chart/viz to be taken serious, it must have the source of the data attributed.

This PR add ability to define source either as a link via data-source attribute on chart div (html) or as a source object in the metadata section of chart data (python). The second method also offer ability to separate the link and display title

<div id='' ...... data-source='https://link'></div>

OR

data['metadata']['source'] = {
    'title': 'Source Title',
    'link': 'https://link',
}

Type of change

Please delete options that are not relevant.

• [X] New feature (non-breaking change which adds functionality)

Screenshots

Checklist:

• [X] My code follows the style guidelines of this project
• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation

[DavidLemayian]

@kilemensi I guess resolve conflict and merge. :)