Add the possibility to load multiple videos

[GiulioRomualdi]

This PR allows the possibility to load several videos from the same dataset. The filenames of each video are retrieved thanks to a RegExp. If we assume that the name of the dataset is dataset.mat the regexp will be

dataset_[a-zA-Z0-9_]*\.mp4$

where

• dataset_ matches the characters prefix_ literally (case sensitive)
• Match a single character present in the list below [a-zA-Z0-9_]
  • * matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
  • a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
  • A-Z matches a single character in the range between A (index 65) and Z (index 90) (case sensitive)
  • 0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
  • _ matches the character _ with index 9510 (5F16 or 1378) literally (case sensitive)
• \. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
• mp4 matches the characters mp4 literally (case sensitive)
• $ asserts position at the end of a line

In other words, dataset_camera1.mp4 dataset_webcam12.mp4 will be considered valid filenames. On the other hand, dataset1_camera1.mp4 will not.

Accordingly to the number of videos opened the layout of the application automatically adds the tabs in the associated layout.

In the following example, I duplicated the video to show the feature

https://user-images.githubusercontent.com/16744101/173373344-a78757ab-2c3e-455b-a19c-e774420da743.mp4