Comment out FPF repo setup in deb builder script

I did this for two reasons:

1. We aren't using any packages from the repo to build the debs at the
moment (if you think about it, that's kind of a catch-22), so commenting
this has no impact on building debs. Also, running `apt-get update`,
which is relativley slow, for no reason is a waste of time.

2. During testing, this created a catch-22 where I wanted to build the
debs so I could add them to the repo and publish the snapshot, but this
deb builder script wouldn't run unless the repo already existed.

We may be able to remove this code entirely, but I decided to leave it
in for now in case it is useful for something that I didn't recognize.
securedrop-grsec metapackage version should match grsec version

Previously the `Version:` of the securedrop-grsec kernel metapackage was
tracking the SecureDrop/securedrop-app-code version. Since the
metapackage tracks the grsecurity upgrades, and is independent of the
version of SecureDrop, it makes sense for the version of the metapackage
to match the grsecurity version.

Updated the deb builder (which we currently only use to build
securedrop-grsec) to get the version for the filename from the Debian
control file. This is important, since in my testing aptly refused to
add two packages with the same filename to the same repo (even if their
`Version:`s were different).

Also makes `build_meta` slightly more generic, to fit its name and
intended purpose. Also changed some variable names for clarity.
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.
Added instructions for downlaoding and verifying the FPF master signing
key. I need @ageis to update this document later on with the correct
link to the key on the FPF website.
Fix indentation
As discussed in #744, it is OK to TOFU the SSH fingerprints for the
Application Server and the Monitor Server. This commit removes the TODO
item from the guide and resolves #744, it also adds consistency to the
ssh-copy-id and ssh examples.
Indentation should be consistent with the rest of the docs
Plural pronouns and small edit
This update documents the accounts, passphrases and two-factor secrets
that will be provisioned during a SecureDrop installation. Closes #759.
Move journalist workstation setup out of docs/install.md and into
tails_files/README.md, closes #747.
Fixed the formatting in tails_files/README.md
Move the section that talks about creating a GPG key for the journalist
from tails_files/README.md to docs/journalist_user_manual.md, be
consistent with headlines in docs/journalist_user_manual.md
Remember that the Document Interface runs on port 8080, if you forget to
add this to the URL you will not be able to connect.
Clarify which Tails device we're talking about and use the word
"credential" instead of "passphrase" when talking about two-factor auth
secrets.
Merge branch 'develop' of https://github.com/freedomofpress/securedrop into develop
Updated install.md to include a step where the admin also sets up
two-factor authentication on Android or iOS for use with the App Server.
Updated with instructions for setting up google authenticator on iOS by
scanning a barcode.
Android barcode scanning instructions
Merge pull request #1 from ageis/develop

Android barcode scanning instructions
Nitpick on @ageis' edits to the google_authenticator doc.