Revert "Added background image resources."

This reverts commit 67bdfce1a22ddb508c01256a8b4fabf4a67637a5.
Revert c2cd2ab..2f33eca

This rolls back to commit c2cd2abadb3525c9b1b92a8254034c082259ff4f.
Typo
Fixed formatting
Fixed typo
Typo
Reordered/merged some slides, added quick work flow exercise, added presenter notes, tweaked content.
Revised exercise 1, added some template and content revisions.
Added mini-exercise before exercise #2
Added in-slide CSS example, moved inline & internal css slides to extras.
Small updates, added lunchtime exercise and presenter notes.
Separated exercise 5 into two.
Separate exercise 6 into smaller exercises and reordered content.
Revised morning slides, moved void elements to extras.
reformatting, added css organization examples, content revisions.
Revised float example to better demonstrate positioning. Can't see fixed positioning well if page doesn't scroll.  Added exercise to add more content.
Revised positioning exercise, added presenter notes.
Home page exercise updates.
Moved sticky footer to "homework". Small content revisions overall.
updated example files for sticky footer