Pin latest/selected post in place of hero

[rosnovsky]

Add the ability to arbitrarily pin any post at hero (on home page). The remainder of posts should go below in a 3x1 grid.

• [x] Replace hero with a post filtered by latest post date
• [x] Remove latest post from the post grid below

[rosnovsky]

@bawbgale @DimitriKourouniotis I've made this update to make it so that there's a way to pin a post to hero area on the home page. To make it happen, just add pin_to_hero: true to the post metadata. The post, it's excerpt and cover image will go the home page hero area. As of this moment, "Introduction to Tableau Prep Pointers" is pinned to the home page.

I've made a wiki page for your reference.

Also, I get easily lost in emails, so ideally, all web dev tasks would go to the project here.