Updated Grid component

Status: **Opened for visibility**
Reviewers: @jeffkamo @ry5n

## Changes
- Moved from a padding based grid system to a margin and relative position based one. This makes it easier to attach the grid directly to elements instead of needing to wrap them in a parent. 

## Notes
- Feel like there might need to be a method for saying "in portrait, be this. in landscape, be this". Our old mixin did this and it was pretty useful.