[apps/src, openni files] Inconsistencies in the command line args

[filbert14]

Now that #5475 is closed, I hope to able able to make following changes:

As several maintainers pointed out, currently,

1. Several files require you to input -h to be able to get the output of usage(), some allow -h and --help
   (compare openni_3d_convex_hull.cpp and openni_voxel_grid.cpp)
2. The variable name arg is used for both device_id and -h or --help
   (see openni_3d_convex_hull.cpp)
3. For some files, --help or -help can only be used to call usage() if they are the first arguments in the cmd line, some use pcl::console::find_argument(argc, argv, "-h"), where it could be anywhere (same example as 1.)
4. options is shown for the output of usage() for some files where no options can be given
   (compare openni_3d_convex_hull.cpp and openni_ii_normal_estimation.cpp, where options is not displayed if options can't be used in main().

Idea:
So that everything says uniform, use std::string device_id instead of std::string arg exclusively for the device id, make it have to be at argv[1] (while checking if it begins with '-' as to not confuse it with options parameter -> see openni_planar_convex_hull.cpp), initialize it to the default value "" so that device_id can safely be passed everytime (grabber looks for first device), allowing it to be optional when its not a cmd line arg and separate it completely from -h or --help (can be at any position, using pcl::console::find_argument(argc, argv, "-h") bzw. pcl::console::find_argument(argc, argv, "--help"))

+Make small changes by deleting options in usage() where none can/needs to be passed

I think it would be a good idea to start with the same files worked on the last time:

apps/3d_rec_framework/src/tools/openni_frame_source.cpp
apps/src/openni_tracking.cpp
apps/src/openni_boundary_estimation.cpp
apps/src/openni_klt.cpp
apps/src/openni_organized_edge_detection.cpp
apps/src/openni_mls_smoothing.cpp
apps/src/openni_uniform_sampling.cpp
apps/src/openni_ii_normal_estimation.cpp
apps/src/openni_grab_images.cpp
apps/src/openni_voxel_grid.cpp
apps/src/openni_feature_persistence.cpp
apps/src/openni_3d_concave_hull.cpp
apps/src/openni_fast_mesh.cpp
apps/src/openni_planar_convex_hull.cpp
apps/src/face_detection/openni_frame_source.cpp
apps/src/openni_planar_segmentation.cpp
apps/src/openni_color_filter.cpp
apps/src/openni_3d_convex_hull.cpp
apps/src/openni_mobile_server.cpp

[mvieth]

Sounds good, feel free to open a pull request 👍

[mvieth]

I assume your pull request fixes this issue, please correct me if I am wrong.