Added first UI elements

Rules can be created from the UI
Game can be stopped/started from the UI
Current level can be reset (Load from file again)
Added "Game" target and main file

TODO (A lot):
 - Unit tests
 - Fully functionnal UI
 - Win conditions
 - Level background
 - Level switching/progression
 - Interesting and varied rules
 - Multi-scale pathfinding
 - etc

CMakeLists.txt

@@ -6,6 +6,7 @@ set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake_modules" ${CMAKE_MODULE_PATH})
 
 add_subdirectory(src)
 add_subdirectory(tests)
+add_subdirectory(game)
 
 # Detect and add SFML
 find_package(SFML COMPONENTS system window graphics network audio REQUIRED)
@@ -13,6 +14,12 @@ if(NOT SFML_FOUND)
     message(FATAL_ERROR "SFML could not be found")
 endif()
 
+# Detect and add TGUI
+find_package(TGUI REQUIRED)
+if(NOT TGUI_FOUND)
+    message(FATAL_ERROR "SFML could not be found")
+endif()
+
 # Detect and add GTest
 find_package(GTest REQUIRED)
 if(GTest_FOUND)