TUTORIAL: 2.5 Labels

[jongund]

https://teachaccess.github.io/tutorial/#/6

I suggest:

1. Renaming this section 2.5 Form controls and just talk about stand form controls
2. Move the aria labeling techniques to another section/slide
3. Include FIELDSET/LEGEND example with a radio button group
4. Discuss the importance of using the LABEL element to increase the effective selection
5. Also have examples for INPUT[TYPE=IMAGE], INPUT[TYPE=BUTTON]
6. Using the HTML5 required attribute for required form controls