Split scss placeholders and mixins
Add basic goal card and styles

Styles are just mushed in to `goals/_goals.css.scss` for now
Add avatar size variations

This also decreases the default avatar size
Revise Goal card styles

This commit adjusts the positioning of the goal title and description.
It also changes all padding + margins to use rhythm units
Linkify Goal card avatar and owner name
Linkify goal critical mass
Basic changes to goal creation form
Separate goal card styles in to separate file
Basic formatting for `goal/show`