This is needed to make shortcode users happy with the new multilanguage support,
but it will also solve many other related posts about "stuff not available in the shortcode".
We will have to revisit this re the handler chain at some point, but that will be easier
now as the integration test story has improved so much.
As part of this commit, the site-building tests in page_test.go is refreshed, they now
tests for all the rendering engines (when available), and all of them now uses the
same code-path as used in production.
Fixes#1229Fixes#2323
Fixes ##1076
Work In Progress!
This commit makes a rework of the build and rebuild process to better suit a multi-site setup.
This also includes a complete overhaul of the site tests. Previous these were a messy mix that
were testing just small parts of the build chain, some of it testing code-paths not even used in
"real life". Now all tests that depends on a built site follows the same and real production code path.
See #2309Closes#2211Closes#477Closes#1744
