Make better use of title and description

In content/_index.en.md

• title is set so that search engines and social media services will display the home page title more nicely;
• The "Get an Edge in Editing" text cannot be the page description because it will be shown in search results and sharing cards, while it does not describe the site well. We should let .Site.Params.description be shown instead.
• Since title is changed, the menu item needs to get a name, the "Kate" text to be shown on page also needs to be in another field.

This goes with aether-sass!36 (merged)

@carlschwan