Resolve "Remove CMake files from core/feature and core/factor"

Closes #247 (closed)

src/factor/CMakeLists.txt

-INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR})
-
-#=========================================
-#=========================================
-# Add in this section the CONDITIONAL CLUES [IF/ELSE]  
-# for external libraries and move inside them the respective lines from above.  
-
-IF (OPENCV_FOUND AND Apriltag_FOUND)
-  SET(HDRS_CONSTRAINT ${HDRS_CONSTRAINT}
-    ${CMAKE_CURRENT_SOURCE_DIR}/constraint_autodiff_apriltag.h
-      )
-ENDIF(OPENCV_FOUND AND Apriltag_FOUND)
-
-#=========================================
-#=========================================
-
-SET(HDRS_CONSTRAINT ${HDRS_CONSTRAINT}
-  ${CMAKE_CURRENT_SOURCE_DIR}/factor_autodiff_distance_3D.h
-  ${CMAKE_CURRENT_SOURCE_DIR}/factor_autodiff_trifocal.h
-  ${CMAKE_CURRENT_SOURCE_DIR}/factor_diff_drive.h 
-  )
-
-SET(SRCS_CONSTRAINT ${SRCS_CONSTRAINT} 
-  )
-
-# Forward var to parent scope
-# These lines always at the end
-SET(HDRS_CONSTRAINT ${HDRS_CONSTRAINT}  PARENT_SCOPE)
-SET(SRCS_CONSTRAINT ${SRCS_CONSTRAINT}  PARENT_SCOPE)
-
-  
\ No newline at end of file