Rename chroot browser data files.
Refactor chroot browser configuration steps.
Bail out properly due to chroot mount errors.
Make sure extensions are symlinked, not copied.

We could use `cp --no-dereference` before, when the TBB_EXT dir only
contained symlinks. This will reduce the memory footprint of the
chroot browsers, and incidentally fixed a bug where the
unsafe-browser's name wasn't set since we copied the langpack before
we fix the name in it.
Use helper function.
Be more aggressive when tearing down chroots.

This way the chroot browsers will close faster.
Reorganize chroot browser scripts.

No code is deleted/added/modified, only moved.
Improve variable name and add quoting.
Add comments about imports.
Add status message for chroot browser exit.
Use unique dot-config directories for the chroot browsers.

It makes a bit of sense on its own, and it guarantees that no weird
cruft in ~/.tor-browser will interfere for whatever reason.
Set nonsense DNS server for I2P Browser.

So there's no chance it will try to use the Torified DNS server, in
case our firewall fails.
Use quoting on variable and assignment values more consistently.