Move session into //blimp/client/app and update GN files.

blimp/client/core/input/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 source_set("input") {
-  visibility = [ "//blimp/client/*" ]
+  visibility = [ "//blimp/client/core/*" ]
 
   sources = [
     "blimp_input_handler_wrapper.cc",
     "blimp_input_handler_wrapper.h",
     "blimp_input_manager.cc",
     "blimp_input_manager.h",
   ]
 
   deps = [
     "//cc/",
     "//ui/events/gestures/blink",
   ]
 
   public_deps = [
     "//base",
     "//third_party/WebKit/public:blink_headers",
     "//ui/events:gesture_detection",
     "//ui/events/blink",
   ]
 }