Create sample project
App now demonstrates some different use cases

It works nicely, and as expected with a nav controller present, but a
tab controller doesn't work properly on its own.
Add another example of a plain view controller within a nav controller
Missed a license header
Updates storyboard and adds images for tab buttons
Completed writeup on uiviewcontroller edges

Including creating lots and lots of screenshots.
Merge branch 'days/20-uiviewcontroller-edges'