Feature: Sponsorships

[simonhamp]

This PR adds support for new options to the groups.json structure to allow groups to define sponsorship opportunities, as well as offering instructions for both group organizers and potential sponsors around how this all works.

See screenshots below for examples of how it works.

"sponsorships": {
  "enabled": true,
  "description": "Support our local PHP community",
  "contact_email": "[email protected]",
  "packages": [
    {
      "name": "Gold Sponsor",
      "currency": "USD",
      "amount": 500,
      "benefits": [
        "Logo on all event materials",
        "5-minute speaking slot",
        "Social media mention",
        "Newsletter inclusion"
      ]
    },
    {
      "name": "Silver Sponsor",
      "currency": "USD",
      "amount": 250,
      "benefits": [
        "Logo on event materials",
        "Social media mention"
      ]
    }
  ]
}

Meetup site

World Site - new /sponsorships page