Make footer look good at smaller widths

Don't worry about any widths smaller than 320px. Also, don't worry about the section of the footer with the links, only look at the section with the green background.

• We want the footer green background to always cover 100% of the horizontal area of the footer section.
• At smaller widths, we want each 'section' of the icon footer ("Contact Us", social media icons, UT-Battelle logo, DOE logo) to be displayed on its own row, instead of all in one row.
• We always want all of the "social media icons" to be on the same row.