Simplify local meetup listings, and merge Twitter timelines into one

[dirv]

Twitter / group layout

• Pull in local group data from a data file, _data/meetups.json, rather than having them hardcoded in the index.html file.
• Uses a new two-column layout for Queer Code groups on the left, and Twitter timeline on the right
• The Twitter timeline is now based on a single list of all Queer Code groups combined. This is maintained on the @qcldn account: https://twitter.com/QCLdn/lists/tweets-from-queer-code
• Twitter links now show in both desktop and mobile views

Hero banner

• Image is adjusted so that it appears straight
• Added a pink background highlight to pull it apart from the places and twitter feeds
• Removed the 'Places' title

This fixes #49.

[dirv]

@chromy Thanks for that - I've reverted the hero change for now as it's addressed in #52.