Made changes to HTML for organization

* Added a headings div to wrap text at top
* Added links to each shape using ids
* Added ids to each shape for use as fragment id for url
* Added fixed position link to go back to the top of the page
* Adjusted CSS to make more responsive, changed media query
Made changes to shapes.css

* Added comments for organization
* Set margins and spacing for shapes container
* Styled link back to top
* Adjusted base class spacing/margin
* Styled links when visited and unvisited