[CMake] Switched to bincrafters modular boost conan packages.

Bumped Boost to 1.66.0.

https://bincrafters.github.io/2017/09/22/boost-modular-packages-conan/

scripts/cmake/ConanSetup.cmake

@@ -31,7 +31,8 @@ endif()
 include(${PROJECT_SOURCE_DIR}/scripts/cmake/conan/conan.cmake)
 
 set(CONAN_REQUIRES
-    Boost/1.64.0@conan/stable
+    boost_optional/1.66.0@bincrafters/stable
+    boost_property_tree/1.66.0@bincrafters/stable
     Eigen3/3.2.9@bilke/stable
     VTK/8.1.1@bilke/stable
     CACHE INTERNAL ""

scripts/cmake/Find.cmake

@@ -60,8 +60,10 @@ find_program(MODULE_CMD modulecmd
 ######################
 ### Find libraries ###
 ######################
-find_package(Boost REQUIRED)
-include_directories(SYSTEM ${Boost_INCLUDE_DIRS})
+if(NOT OGS_USE_CONAN)
+    find_package(Boost REQUIRED)
+    include_directories(SYSTEM ${Boost_INCLUDE_DIRS})
+endif()
 
 find_package(VTK 8.1.0 REQUIRED)
 include(${VTK_USE_FILE})