clean up plugin store when removing data instead of setting the value to nil.
Add rel=next to next page link for crawlers
Admin Quick Start Guide topic is visible only to staff in new sites
clean up plugin store when removing data instead of setting the value to nil and do it a reasonable way.
Merge pull request #2005 from eriko/plugin_store_delete

clean up plugin store when removing data instead of setting the value to...
Add previous page link for crawlers
Oops, I meant 1
BUGFIX: force tar to follow symlinks during the export
unnecessary CSS suppression of li paras
FIX: Bunch of Onebox issues
Revert "FIX: Bunch of Onebox issues"

This reverts commit ccbe671e4ad86d44c78f6232a2a61b9ca8e849d2.
FIX: DiscourseLocalOnebox is used!
FIX: DiscourseLocalOnebox should have a higher priority than other
discourse sites
FIX: Margin in onebox
Remove unnecessary image.
Merge pull request #2008 from techAPJ/update-docker-guide

Remove irrelevant image.
Generalize the guide
Merge pull request #2009 from techAPJ/update-docker-guide

Generalize the guide
Allow the `customHTML` helper to look up fragments outside of the
preloadStore, so plugins can stuff HTML in there when overriding a whole
template doesn't make sense.
Hooks for extra nav items.