Restructure to make it easier for new students

[tamouse]

Referring to gdiminneapolis/html-320-stylin-with-sass-project-files#2

The class exercises require the command line and Git to do anything useful. This is too hard for the typical GDI student to generally handle, and disrupts the class when things don't work as expected. Trying to reconcile the tools between the different platforms and versions is just not working.

Proposal

Use GUI tools for everything

• SourceTree
• CodeKit or Prepros
• Atom

Organize the exercises in separate directories, instead of branches in the project. This likely means it will be necessary to create a different repository for the exercises, but they could be fairly easily included in the same repo as the slides.

Changes listed will also require changes to the slides as far as giving instructions.