Add possibility of a custom CSS for a community

[BradHN1]

User Story

As a Community Admin with the MassEnergize pages embedded in their website
I want to modify a subset of CSS styles
So that the page styles match the website better

Additional details/context

Patrick Vallaeys from Harvard MA requested the ability to modify some CSS styles for their community pages. He could supply a link to a CSS file they have hosted with their wordpress site. He would like to have a couple styles override the ones we have to customize title and footer widths, colors. And disable the breadcrumb bar

Value added

This would be one way to customize some styles. Not something most community admins would be able to do or want to do.

Acceptance criteria

1. the additional CSS Styles would override the default styles in our css files.
2. We should make a test CSS to validate this functionality, changing some colors.