[software] SfM: features/matchesFolders are no more required

When computing a SfM node from a previous SfM, the features/matches are
not needed.

src/software/pipeline/main_incrementalSfM.cpp

@@ -101,13 +101,14 @@ int main(int argc, char **argv)
       "SfMData file.")
     ("output,o", po::value<std::string>(&outputSfM)->required(),
       "Path to the output SfMData file.")
-    ("featuresFolders,f", po::value<std::vector<std::string>>(&featuresFolders)->multitoken()->required(),
-      "Path to folder(s) containing the extracted features.")
-    ("matchesFolders,m", po::value<std::vector<std::string>>(&matchesFolders)->multitoken()->required(),
-      "Path to folder(s) in which computed matches are stored.");
+    ;
 
   po::options_description optionalParams("Optional parameters");
   optionalParams.add_options()
+    ("featuresFolders,f", po::value<std::vector<std::string>>(&featuresFolders)->multitoken(),
+      "Path to folder(s) containing the extracted features.")
+    ("matchesFolders,m", po::value<std::vector<std::string>>(&matchesFolders)->multitoken(),
+      "Path to folder(s) in which computed matches are stored.")
     ("outputViewsAndPoses", po::value<std::string>(&outputSfMViewsAndPoses)->default_value(outputSfMViewsAndPoses),
       "Path to the output SfMData file (with only views and poses).")
     ("extraInfoFolder", po::value<std::string>(&extraInfoFolder)->default_value(extraInfoFolder),