Change date format

The "published on" date sometimes appeared below the post-title and sometimes it appeared above it. I wanted to fix this small inconsistency. I also wanted to take this opportunity to make the date format a bit more natural by removing the leading zero from the date and writing out months in full.

User story

As a user, I need to know when an article was written, to help me decide if the content is still relevant.

Acceptance criteria

• Date format is changed from 01 Jan 2018 to 1 January 2018 to match the GDS content style guide
• Use the Shopify Liquid and STRFTIME resources to control the date format
• Date is moved below the title on post pages