Several fixes for Mac

These fixes should be useful for all, even non-Mac.

They relate to either forgotten #includes, forgotten override keywords, or forgotten const keywords. They all caused compilation errors in my MacBook.

CMakeLists.txt

@@ -290,7 +290,8 @@ SET(HDRS_FACTOR
   include/core/factor/factor_base.h
   include/core/factor/factor_block_absolute.h
   include/core/factor/factor_diff_drive.h
-  include/core/factor/factor_epipolar.h
+#  include/core/factor/factor_epipolar.h
+#  include/core/factor/factor_feature_dummy.h
   include/core/factor/factor_fix_bias.h
   include/core/factor/factor_odom_2D.h
   include/core/factor/factor_odom_2D_analytic.h