big_pipe 8.x-1.0

Includes the changes that were necessary to make BigPipe core-worthy, and all commits to BigPipe after it got committed. BigPipe is included in Drupal 8.1.0.

Changes since 8.x-1.0-rc1:

• #2710045 by Wim Leers: Disallow the use of the BigPipe contrib module in Drupal >=8.1.0, only allow Drupal 8.0.x
• #2702537 by ifrik, Wim Leers: Update the BigPipe module description to be in line with the Help text standard
• Follow-up for issue #2678568 by Wim Leers: Ensure good UX & DX even when A) rendering of placeholder fails, B) some response event subscriber fails
• #2678568 by Wim Leers: Ensure good UX & DX even when A) rendering of placeholder fails, B) some response event subscriber fails
• #2670444 by Wim Leers: Embedded AJAX responses aren't application/json, but application/vnd.drupal-ajax
• #2679867 by Wim Leers, mr.baileys: BigPipe causes PHP notices with JavaScript disabled on error pages
• #2678628 by Wim Leers: Consider removing the BigPipe no-JS cookie when JS is enabled again in a browser
• Comment 263: Improve BigPipeInterface documentation.
• Comment 262: Fix nitpicks and add BigPipe::filterEmbeddedResponse() helper method.
• Comment 250: Fix nitpicks.
• Comment 245: Bring back work-around for routes not being rebuilt in time, until #2589967 is fixed.
• Comment 243: simplify BigPipeTest::assertSetsEqual().
• Comment 242: _no_big_pipe route option instead of hardcoding the special casing of the Batch & Module Installation routes.
• Comment 232: Forgot to update unit test in previous comment/commit.
• Comment 230: Special case the Batch & Module Installation routes.
• Comment 218: add BigPipeMarkup, don't use \Drupal\Core\Render\Markup; use HTTP 400 instead of 500.
• Comment 216: Work around the router being rebuilt to late, core bug #2589967.