minor updates
changes to class 3 and 4

mods on class3.html, class4.html
add exercises/class3/styles.css
add class3exercise.jpg to images
add example-blockinline.png
deleted personal image
updates to class4.html
Merge branch 'gh-pages' of https://github.com/gdi-tri-cities/gdi-core-html-css into gh-pages

Conflicts:
class4.html
revert to changes