debian/rules: Fix license & copyright

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
debian/control.d/control.in: Bump standards-version to 3.9.5.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
debian: Update to 3.5.1 final

Update the submodule to 3.5.1, and also extend the Debian changelog to
mention some of the new major features.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
debian/control.d/control.in: Adjust the syslog-ng-core Suggestions

The syslog-ng-core package should suggest all of the modules, core and
optional ones alike.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>