Merge pull request #756 from runasand/develop

Remove Authy, as discussed in #752
Update repository domain to freedom.press
Merge pull request #757 from ageis/develop

Update repository domain to freedom.press
Decided to clean up the section about USBs, DVDs and CDs, also updated
the section that talks about setting up the Admin USB with links to
instructions on the Tails website. Closes #741.