CSS Class name standardization

## Is your feature request related to a problem?
**Please describe.**
As @johnhenley mentioned before the use of CSS classes is a bit of a mess.
I don't suggest we o over all classes and change them, but I think we should use a standard for anything new or refactored

## Describe the solution you'd like
We already added a wrapper class in v8: dnn-community-forums

1, I suggest we start all used classes with "dcf" to avoid clashed with other CSS, unless we are using a generic DNN component.

so
dcf-grid
dcf-header
etc.

2. Use a dash between "words
3. All lowercase

## Describe alternatives you've considered
None