gtest: move GTest/GMock files to separate directory, update GTest/GMock usages

* all GTest/GMock files moved to `test/gtest` directory
* `CMakeLists.txt` created in `test/gtest` from `CMakeLists.txt` in `test`
* GTest/GMock target in CMake renamed to `gtest` (was `gmock`)
* CMake `gtest` target updated to export includes as "gtest/gtest.h" or "gmock/gmock.h" only
* includes in tests updated: "gtest.h" -> "gtest/gtest.h", "gmock.h" -> "gmock/gmock.h"
* removed duplications of `target_include_directories` for GTest/GMock directories (CMake manages them)

test/gtest/CMakeLists.txt

@@ -0,0 +1,33 @@
+#------------------------------------------------------------------------------
+# Build the google test library
+
+# We compile Google Test ourselves instead of using pre-compiled libraries.
+# See the Google Test FAQ "Why is it not recommended to install a
+# pre-compiled copy of Google Test (for example, into /usr/local)?"
+# at http://code.google.com/p/googletest/wiki/FAQ for more details.
+add_library(gtest STATIC
+  gmock-gtest-all.cc gmock/gmock.h gtest/gtest.h gtest/gtest-spi.h)
+target_compile_definitions(gtest PUBLIC GTEST_HAS_STD_WSTRING=1)
+target_include_directories(gtest SYSTEM PUBLIC .)
+
+find_package(Threads)
+if (Threads_FOUND)
+  target_link_libraries(gtest ${CMAKE_THREAD_LIBS_INIT})
+else ()
+  target_compile_definitions(gtest PUBLIC GTEST_HAS_PTHREAD=0)
+endif ()
+
+target_compile_definitions(gtest PUBLIC GTEST_LANG_CXX11=1)
+
+if (MSVC)
+  # Disable MSVC warnings of _CRT_INSECURE_DEPRECATE functions.
+  target_compile_definitions(gtest PRIVATE _CRT_SECURE_NO_WARNINGS)
+  if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    # Disable MSVC warnings of POSIX functions.
+    target_compile_options(gtest PUBLIC -Wno-deprecated-declarations)
+  endif ()
+endif ()
+
+# Silence MSVC tr1 deprecation warning in gmock.
+target_compile_definitions(gtest
+  PUBLIC _SILENCE_TR1_NAMESPACE_DEPRECATION_WARNING=1)