Prepare 2.7

CHANGELOG.md

-# Master (will become release 2.7)
+# Release 2.7
 
 * The header `lagrange.hh` now includes all headers of all Lagrange implementations,
   not just the ones with run-time order.

dune.module

 Module: dune-localfunctions
-Version: 2.7-git
+Version: 2.7.0
 Maintainer: dune-devel@lists.dune-project.org
-Depends: dune-geometry (>= 2.6)
+Depends: dune-geometry (>= 2.7)
 Whitespace-Hook: Yes