Improve dataset sharing and discoverability by adding SEO meta tags

[rufuspollock]

As X who wants to share a dataset on social media or in gitter etc I want to have a summary of the dataset along with a link to datahub stuff like an image (if exists) so that people know what this is

As DataHub Community member I want to improve the discoverability of my datasets by search engines

<meta name="description" content=""/>
<meta property="og:title" content="...">
<meta property="og:description" content="...">
<meta property="og:site_name" content="DataHub">
<meta property="og:image" content="">
<meta property="og:url" content="https://datahub.io/...">
<meta property="twitter:card" content="player"/>
<meta property="twitter:site" content="@datahubio"/>
<meta property="twitter:account_id" content="TODO"/>
<meta property="twitter:description" content=".."/>
<meta property="twitter:title" content="..."/>
<meta property="twitter:image" content="..."/>

[AcckiyGerman]

TESTED & FIXED

• dataset's pages now contain the meta information including dataset's title and description.