Merge pull request #22 from marcussaad/gh-pages

Images on a few slides
fix video code in sample track
add subheader to what is webvtt
remove center on code class
add js code - get track element, create texttrackcue, add remove cues
add subheader to why do we need webvtt
change visually impaired users to impaired users
change title of what can we do with webvtt
remove cue id from WebVTT File in Action slides
change DOM api headings to h1
Fixed navigation bar slide-17