Update standard_layout.html.twig

Check existence of admin_pool in some missing places.
Don't show filters container when no one is active or visible
Merge pull request #2449 from costyoancea/patch-1

Added missing checks for admin_pool in standard_layout.html.twig
Merge pull request #2478 from juherpin/ftr-displayable-filters

Don't show filters container when no one is active or visible
add documentation and option to overwrite some templates
add support for form/filter theme overwrite
improve select2 layout
Merge remote-tracking branch 'origin/master'
Merge remote-tracking branch 'origin/master'