Twenty Seventeen: Update page column setting

[melchoyce]

Right now the page column setting is hidden when you have widgets in the Sidebar widget area. Since pages don't ever display the Sidebar widget area, the setting shouldn't be effected by it.

The description should be updated to:

You can opt to display all pages with a one column or two column layout. When the two column layout is assigned, the page title is in one column and content is in the other.

That does leave the question of archive pages. I think that if you don’t have widgets in the Sidebar widget area, the columns setting should probably also apply to archives — but if you do have widgets in the Sidebar widget area, the setting should be ignored on archive pages.

[celloexpressions]

First pass for customizer.

[celloexpressions]

38538.0.diff​ covers the customizer; archives need updates in the CSS to allow for a one-column option. I'm going to leave that part for @laurelfulford since I'm less familiar with that.

I ended up taking the pages part out of the description as well, as it's not really accurate. We may need to continue iterating here.

[laurelfulford]

In 38538.1.diff​ I added some styles to make sure the archives also apply the one column layout when that option is selected and there are no sidebar widgets assigned.

[davidakennedy]

In 39078:

Twenty Seventeen: Update page layout setting for all use cases

• Makes sure the page layout setting also applies to pages, and is not completely hidden from them when a sidebar widget is present. Pages do not have a sidebar, so that was incorrect.
• Updates description in Customizer for brevity and accuracy.
• Applies setting to archive pages as well.
• Updates CSS to reflect changes.

Props celloexpressions, laurelfulford.

Fixes #38538.