Add favicon, and while at it, OG and Twitter Card tags

[danrademacher]

@nilesbarnes asked via email about adding ECG favicon to the site.

Should be able to steal code and links from https://www.greenway.org/

• [x] Favicon

For favicon, looks like these lines (made links absolute):

  <link rel="apple-touch-icon" sizes="180x180" href="https://www.greenway.org/favicons/apple-touch-icon.png">
  <link rel="icon" type="image/png" sizes="32x32" href="https://www.greenway.org/favicons/favicon-32x32.png">
  <link rel="icon" type="image/png" sizes="16x16" href="https://www.greenway.org/favicons/favicon-16x16.png">
  <link rel="manifest" href="https://www.greenway.org/favicons/manifest.json">

Not sure if we can just refer to items on another server for favicons. If so, I assume this is cut and paste. If not, would need to download the images and store with our code base, which also sounds pretty easy.

• [x] Social Tags

For social, I see that our code has OG and Twitter Card blanks already present. Here's that block of code with content, plus added some other OG tags for image sizing based on what's present and working at greenway.org

    <!-- Social Media: FB -->
    <meta property="og:url" content="https://map.greenway.org">
    <meta property="og:title" content="East Coast Greenway Map">
    <meta property="og:description" content="Use this map to plan routes along the East Coast Greenway, all the way from Florida to Maine.">
    <meta property="og:image" content="https://www.greenway.org/imgs/og.jpg">
    <meta property="og:image:type" content="image/jpg" />
    <meta property="og:image:width" content="1200" />
    <meta property="og:image:height" content="630" />

    <!-- Social Media: Twitter -->
    <meta name="twitter:card" content="summary">
    <meta name="twitter:site" content="ECGreenway">
    <meta name="twitter:creator" content="ECGreenway">
    <meta name="twitter:title" content="East Coast Greenway Map">
    <meta name="twitter:description" content="Use this map to plan routes along the East Coast Greenway, all the way from Florida to Maine.">
    <meta name="twitter:image" content="https://www.greenway.org/imgs/og.jpg">
    <meta name="twitter:image:alt" content="East Coast Greenway Logo">

[clhenrick]

@danrademacher added these, let me know if they look correct?

[danrademacher]

Verified favicon in Chrome:

Twitter Card using https://cards-dev.twitter.com/validator

Note that Facebook Image Was not appearing as expected, but then a few minutes later, presto:

Must be a lag in their system, though I even used the FB OPG Debugger's "Scrape Again" to no avail.

Anyway, all looking good!