Clean up site and remove outdated information

[angelsl]

Closes #269. Closes #164 (the Code page is removed).

Things to do after this:

• Create a site/page for Hacker Tools
• Feature our publicity channels more prominently (Add discord link somewhere prominent, e.g. header #128, As a user, I want to see social media links to our social media channels #59, etc)
• Slight reorganisation; currently some pages are only accessible via links in the middle of prose. Figure out somewhere to link this pages
  • Friday Hacks schedule (/fridayhacks/schedule)
  • Recordings
• Filter out Friday Hacks posts from the post listing in homepage (As a user, I want to see relevant blog posts on the front page #54)

[nushackers-org]

Deploy preview for nushackers ready!

Built with commit 0509928

https://deploy-preview-271--nushackers.netlify.com

[angelsl]

Summary of changes:

• Remove references to code.nushackers.org
• Remove separate Events page; the menu item now links to a section in About
• Feature Hacker Tools on the homepage (replacing code@NUS), although it currently does not link anywhere
• Change Discussion to Community, and update the links
• Update "What we do" in About, and the About Friday Hacks page
• Converted HTML to Markdown in the old ported single pages where possible
• Made the text sound a bit friendlier where possible
• Removed Title Case where it is not something copied from elsewhere