Minor changes in reading config files and determining calib_dir

[j-ullrich]

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I only changed some minor things, that don't change any functions but maight prevent errors for other users.

In Pose2Sim.py, the method for loading configuration files did not work when there was a file sorted before Config.toml. It now explicitly loads the Config.toml file.

In personAssociation.py and triangulation.py, the config_dir could not be determined correctly if there was a file sorted before the directory. It now only considers directories.

[davidpagnon]

Hi, thank you for your pull request!

• As for replacing toml.load(os.path.join(root, files[0])) with toml.load(os.path.join(root, 'Config.toml')), I initially did it because I wanted the user to be able to run Pose2Sim.triangulation('my_own_config_number_64.toml') and release the constraint on the Config name. The way you did it adds a constraint on the name of the Config file, but releases the constraint that no other file needs to be in the same folder. I honestly don't know what is best. What do you think?
• Good idea about only considering directories!