[Issue #624] Add React slides to main curriculum list

[thefishter]

Add React course to curriculum list

Fixes issue #624

Here's a description of changes:

• Add REACT101: Intro to React.js listing to curriculum list on main index.html
• Link to external slides ('Lesson Plan') as well as 'Meetup description' and 'Follow Up Email'
• Remove dead "links"

cc @gdisf/admins

[verythorough]

Deploy preview for teaching-materials ready!

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