Sort out meta og:image and meta twitter:image

[julianorchard]

Two tasks for this really;

• Create a default location, like /res/default.jpg which could be used as a default input for <meta name="twitter:image" and <meta property="og:image".
• REMOVED THIS: Check if there's a jpg or png file in '/res/name-of-post/relating to each page, and if there is, use that as<meta name="twitter:imageand<meta property="og:image"`.

I'll also automatically create this location (/res/name-of-post/) upon the posts creation (automate populating that file location??)

[julianorchard]

Instead of having it so it looks in res/name-of-post, just input image normally, which is nice (although I think the previously thought about idea would be neater in the long run...)