consolidate common repositories under "carpentries" github organization

[fmichonneau]

https://github.com/swcarpentry/workshop-template/issues/478

[fmichonneau]

Following today's meeting, the lesson infrastructure committee has decided to move forward on this. I will implement the migration and ensure that:

• privileges are appropriately migrated
• the lesson release scripts and archives don't get broken in the process

[fmichonneau]

This task is completed:

• the repositories have been migrated to the carpentries github organization
• the URLs have been updated in the styles repositories
• the organization websites (datacarpentry.org, librarycarpentry.org, software-carpentry.org) have been edited to use the new URLs where appropriate
• redirects have been implemented in github.com/swcarpentry/swcarpentry.github.io