Add short description instead of excerpts

[secondsleep-blaine]

The excerpt is currently being used to show a short description below the title of the explainer/procedure posts, but a short description included in Front Matter is preferred. This is because the excerpt is often too long for the description that should be displayed and/or is written in an expository manner that doesn't provide an adequate overview.

[secondsleep-blaine]

Added a description property to Front Matter of each post that is used for the excerpt on the service page.