Restructure the project tree for unit testing

Restructure the whole project tree so that the component can be unit tested. Also update some cmake files to update the modified paths, update test cases etc.

app_test/CMakeLists.txt

@@ -0,0 +1,13 @@
+cmake_minimum_required(VERSION 3.5)
+
+# Define component search paths
+# IMPORTANT: We should tell to the ESP-IDF
+# where it can find relay_chn component.
+# We add the 'relay_chn' directory to the COMPONENT_DIRS by specifying: ../relay_chn
+set(EXTRA_COMPONENT_DIRS "${CMAKE_CURRENT_SOURCE_DIR}/../relay_chn")
+
+# Include ESP-IDF project build system
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+
+# Define the name of this project
+project(relay_chn_app_test)