Adds quick screenshot method to all SLElement objects

Reduces steps and allows for easy screenshots of individual
elements. Should be useful in multiple runs for small UI changes.
Updated commit per suggestions on github.

Moved element screenshotting to SLUIAElement class.
Removed file change that affected style
Cleaned up documenation as per suggestions
Merge pull request #129 from jzucker2/screenshot_element

Adds quick screenshot method to all SLElement objects