add excerpt box allowing page excerpts to be set.

[benlk]

Fixes https://github.com/INN/umbrella-sfpublicpress/issues/121

Changes

This pull request makes the following changes:

• Adds the excerpt editing box to the 'page' post type.

This allows page excerpts to be changed, so that pages no longer have the whole post content in the post_excerpt field, which was the root cause of https://github.com/INN/umbrella-sfpublicpress/issues/121

Why

For https://github.com/INN/umbrella-sfpublicpress/issues/121

Testing/Questions

Features that this PR affects:

• editor on pages

Questions that need to be answered before merging:

• [ ] Is this PR targeting the correct branch in this repository?
• [x] Will SFPP have to edit all these pages?
  • Yes.

Steps to test this PR:

1. Find a page with a very long excerpt in search, such as any in http://sfpublicpress.flywheelsites.com/?s=seth+rosenfeld&search+submit=
2. Edit the post, change the excerpt.
3. The updated excerpt should now be visible on the search-results page.

Note that if the excerpt contained the search query, because excerpts containing the search query are prioritized above post content containing the search query, the queried item's position in the search may change if the edited excerpt does not have the search terms.

[benlk]

@MirandaEcho do you want to wait for Josh's review on this, or is it okay to deploy direct?

[MirandaEcho]

@MirandaEcho do you want to wait for Josh's review on this, or is it okay to deploy direct?

If you feel better about having him review first, then Monday AM is fine. If you think it's fine, go ahead and deploy. I trust your judgment!

[benlk]

This is limited enough that I think it's fine.