clean up plugin store when removing data instead of setting the value to nil.
FEATURE: single sign on support

Added support for outsourcing auth to a different website, documentation on meta
Merge pull request #2006 from awesomerobot/master

adding word-wrap: break-word back to usernames, fixing onebox bg in quotes
shorten to "Invite Friends"
deprecate this guide in favor of Docker
link to master install guide
deprecate this guide in favor of Docker
Update INSTALL-email.md
Rename HEROKU.md to install-HEROKU.md
normalize on Docker installs
Update TROUBLESHOOTING.md
clean up DO guide a bit more
2GB vs 1GB
Update INSTALL-digital-ocean.md
readme cleanup
no samsaffron
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...