Render tables as cards on mobile

[derekeder]

Applies card styles for tables in mobile mode as mentioned in datamade/how-to#350

For screens smaller than 768px (xs on Bootstrap 3), table rows are rendered as cards for both meeting agendas and legislative actions:

Meeting agenda:

Legislation action:

This PR also cleans up some redundant css classes and:

• better presents responsive vimeo iframes. related to better event page: vimeo embed, event agenda #359
• logic update for getting source link. fix again for fix web links on bill pages (maybe other pages) #362