Security fixes

• Upgrade Tor Browser to 7.5.3 (MFSA 2018-10, Closes: #15459).

• Upgrade Thunderbird to 1:52.7.0-1~deb9u1.0zerotracepen1 (DSA-4155,
  Closes: #15471).

• Upgrade libicu to 57.1-6+deb9u2 (DSA-4150).

• Upgrade intel-microcode to 3.20180312.1~bpo9+1. Implements
  IBRS/IBPB/STIPB support, Spectre-v2 mitigation for: Sandybridge,
  Ivy Bridge, Haswell, Broadwell, Skylake, Kaby Lake, Coffee Lake
  (Closes: #15173).

• Bugfixes

• Tor Browser AppArmor profile:

  • Grant the main Firefox process access to machine-id: needed for
    IBus support (Closes: #15437).
  • Allow access to extensions installed by the user such as Zero Trace Pen
    Verification (Closes: #15434).

• Remove packages needed to support Video Acceleration API
  (VA-API) because they breaks opening GNOME Settings and Totem in
  Zero Trace Pen 3.6 on some computers (only NVIDIA for now but perhaps
  other hardware is affected). (Closes: #15433, #15449)

• Upgrade Linux to 4.15.11-1 and bump the aufs submodule (Closes:

  15456, #15457).

• zerotracepen-documentation script:

  • open translated documentation page in Tor Browser when online
    (Closes: #15371).
  • use documented syntax for os.execv (Refs: #15332)
  • re-add support for passing a HTML anchor as the second
    argument.

• Fix issue where the zerotracepen-persistence-setup user's guid would be
  changed when it was the uid that was intended (Closes: #15422).