Fix #975 : Reworks avatar sizes and spacing across breakpoints

Created by: beckkramer

This is a fix for Issue #975 (closed)

This PR:

• Adds a height/width Sass mixin for different photo sizes to pare down on code
• Adds a tiny image size and adjusts the other values as some weren't being used
• Adjusts the spacing and orientation of the avatar images per breakpoint

Tasks from the issue:

• Add a tiny photo size to the $_person-photo Sass map.
• Tweak the incorporating breakpoint declarations to incorporate it.
• Verify using a smartphone.

Screenshots of the element at different breakpoints: