Add video player student-facing documentation
Merge pull request #10 from edx/sylvia/docs/DOC-732

Draft of video student-facing documentation
Add download information to video SFD topic
Merge pull request #13 from edx/sylvia/docs/videoupdate

Add download information to video SFD topic
Fix formatting in video topic
Merge pull request #14 from edx/sylvia/docs/vidupdate

Fix formatting in video topic
Fixes DOC-1146, incorrect Show Answer description

@adampalay , @mhoeber @catong , @srpearce
Sylvia's edits