Bootstrap 4 and more controls

[corinis]

I adjusted the code to correctly render the content and adjusted it so it works with bootstrap4.

New controls added:

• card
• carousel
• pull
• jumobtron

Also added support for bootstrap grid by adding

• row
• col and add an option to put a card in a grid (just add {% card col %}..

[wzpan]

@corinis It's there anyway to remove the dependency of marked so as to make these four plugins work on any other renderers?

[corinis]

i inject into the markdown editor because I need to be able to adjust the html output especially for the crd control. I am guessing that markdown-it is extensible as well, so that the renderer for the inline html can be adjusted. Worst case would be to disable these controls if no appropriate renderer is available