Update changelog with latest merges and DSAs.

debian/changelog

 tails (2.7) UNRELEASED; urgency=medium
 
   * Major new features and changes
-    - Install Tor 0.2.8.8. (Closes: #11832)
     - Upgrade Icedove to 1:45.4.0-1~deb8u1+tails1. (Closes: #11854,
       #11860)
 
+  * Security fixes
+    - Upgrade to Linux 4.7. (Closes: #11885, #11818)
+    - Upgrade to Tor 0.2.8.9. (Closes: #11832, #11891)
+    - Upgrade imagemagick to 8:6.8.9.9-5+deb8u5.
+    - Upgrade openssl to 1.0.1t-1+deb8u5.
+    - Upgrade libarchive to 3.1.2-11+deb8u3.
+    - Upgrade bind9 to 1:9.9.5.dfsg-9+deb8u8.
+    - Upgrade c-ares to 1.10.0-2+deb8u1.
+    - Upgrade nspr to 2:4.12-1+debu8u1.
+    - Upgrade nss to 2:3.26-1+debu8u1.
+    - Upgrade tar to 1.27.1-2+deb8u1.
+    - Upgrade mat to 0.5.2-3+deb8u1.
+
   * Minor improvements
     - Ship Let's encrypt intermediate certificate to prepare the
       the next certificate renewal of our website. Also unify the