Add .speaker class

This is the other change to go along with the change to the speakers.html page.
To give a quick example I added two cols at medium and four at large breakpoint.
Because this is in Sass it won't change how the stevenm18.github.io page looks right away when you merge. You will have to

1. Merge the pull request
2. Open github app on your computer
3. Click sync changes to pull changes from github.com (make sure you've cloned the repository first)
4. Open the files in an editor like sublime and make any more changes you want
4. Open Scout and make sure it has a project setup for the repository
6. Check that scout compiled the Sass to CSS
7. Click Sync again in github app to push changes back to github.com
8. check stevenm18.github.io to see if the changes took effect.