Use a script to update workshop posts from repos

[kelly-sovacool]

Changes:

• New Python script to update the workshop posts based on presence of repos with names that start with YYYY-MM-DD.
  • Default behavior: removes posts from prior to the current date and writes upcoming workshop posts.
  • Alternative behavior: write all workshop posts, both past & upcoming.
  • See the README for usage instructions.
• Got rid of the News tab. Probably should only have this if someone can commit to keeping it up-to-date.
• Update the Links page. Filled in some links, removed empty links to tools. We can fill them back in later.
• Add a link to the MCommunity group on the home page.
• Add my (@kelly-sovacool) instructor page.

I did not build the site locally -- something's up with Ruby on my mac -- so you (@pschloss) may want to do that before accepting this PR.