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

Closes #247 (closed)

src/feature/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_FEATURE ${HDRS_FEATURE}
-    ${CMAKE_CURRENT_SOURCE_DIR}/feature_apriltag.h
-      )
-  SET(SRCS_FEATURE ${SRCS_FEATURE}
-    ${CMAKE_CURRENT_SOURCE_DIR}/feature_apriltag.cpp
-      )
-ENDIF(OPENCV_FOUND AND Apriltag_FOUND)
-  
-#=========================================
-#=========================================
-  
-SET(HDRS_FEATURE ${HDRS_FEATURE}
-  ${CMAKE_CURRENT_SOURCE_DIR}/feature_diff_drive.h 
-  )
-
-SET(SRCS_FEATURE ${SRCS_FEATURE}
-  ${CMAKE_CURRENT_SOURCE_DIR}/feature_diff_drive.cpp 
-  )
-
-# Forward var to parent scope
-# These lines always at the end
-SET(HDRS_FEATURE ${HDRS_FEATURE}  PARENT_SCOPE)
-SET(SRCS_FEATURE ${SRCS_FEATURE}  PARENT_SCOPE)
-  
\ No newline at end of file