Added screenshots for all themes

[rben01]

As I was looking through the included themes, the hardest part about choosing a theme was knowing what it would look like without actually applying it. Using the sample page was somewhat cumbersome compared to rifling through screenshots, but the I found the selection of screenshots included in this repo lacking; many themes were missing screenshots, and themes that did have screenshots only covered a portion of the possible page elements.

Therefore I went and took screenshots of every included theme, capturing as much of the test page as I felt was reasonable. Since I automated this with the (very handy) Keyboard Maestro app, I also included the macro I used to accomplish this task.