Add NEST 3.5 release

Switching from nest@3.5_rc1 to the actual release nest@3.5. The minor changes that were made do not require another release candidate round of NEST itself and can directly go into the integration testing of the upcomgin EBRAINS release.

packages/nest/package.py

@@ -26,7 +26,7 @@ class Nest(CMakePackage):
     git      = "https://github.com/nest/nest-simulator.git"
 
     version('master', branch='master')
-    version('3.5_rc1',sha256='0ccc520ff642be4a30c0606150a397e6137362a2acf76ea03a8ee2aa48803a3e')
+    version('3.5',    sha256='4504ff7f9cfa051c91a5e85a0761bdd09d23aeeadac22c45f6be18b7fbe2db43')
     version('3.4',    sha256='c56699111f899045ba48e55e87d14eca8763b48ebbb3648beee701a36aa3af20')
     version('3.3',    sha256='179462b966cc61f5785d2fee770bc36f86745598ace9cd97dd620622b62043ed')
     version('3.2',    sha256='583d5725882ad5e8fd4fc7ffab425da97cbbb91fadbc327e940c184e8892b958')