Switch to ffdhe3072 to enable RFC 7919

The idea being:
- it's a "nothing up my sleeves" group
- it may help shave off some bytes of the SSL handshake; That being
said, I doubt that clients that are modern enough to support this RFC
won't offer an EC kex

https://raw.githubusercontent.com/internetstandards/dhe_groups/master/ffdhe3072.pem

core/nginx/conf/dhparam.pem

@@ -1,11 +1,11 @@
 -----BEGIN DH PARAMETERS-----
-MIIBiAKCAYEAtQlUSOKGjpdXJ154qmMEa1pEs+9CdSxWiZFkiXBJb0lTafOh8cfF
-2IkcWSwzxWwjW4Ad26UQQFh1poGf2QBzVk2vuKCekYzPAs/WqH8VwiXBiWR5R9lh
-v/+CkEBYuQOzAhXLN6ZGdPPa2sjdI49rlaIqyLJE4D0TI/VHYmC/vEwqkJUgaGrS
-19LhHZimnmouvrnyBPyf00czXlMow0RnmYeHVZ7W5hu7t9TH9o3QAN/GKiFfxFj+
-RkdLM7beQdS0He5YeTaElM5l1YT5d5gHFbOzEQyKHd10ux+bgVcgUeVbBnI1SAIC
-w53yc1PkDAiRijSP5j5aWq1djtJPheS13o35HyIf0cHzkNYhKfX5JWPj/cbgdM+C
-FL1bnRc8sL5oxmkDoGJhiNZIf4n2WtS8Zu28gUgat6S+vCm/4yavIc/T1g6UiNKE
-X41HPbsma/QWUwOL6S+b2qr+7rKqjI5TzVek8vBMellEV4mBvfQU3NDSQ4WvxbTq
-ZEOgLPA178nrAgEC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 -----END DH PARAMETERS-----

towncrier/newsfragments/2357.misc

@@ -0,0 +1 @@
+Switch to ffdhe3072, the "nothing up my sleeves" group defined in RFC 7919.