Skip non-directory files in dataset creation (like .gitignore)

[marzzelo]

I propose some minor modifications (which do not affect compatibility with the video tutorial) and avoid a bug during serialization.

• Add max_num_hands parameter to Hands class (set to 1), avoiding erroneous detection of a second hand (this sometimes occurs when the face appears in the frame during sampling).
• (Bug Fix) Skip non-directory files that may be present under ./data folder during dataset creation (like .gitignore)
• Display some status messages during serialization (the system seems frozen when many classes are processed).
• Added .gitignore to exclude the generated pickle file and .venv & IDE cache directories.

[GLWmax]

I would like to use it two-handed, but in your code I kept getting crashes. Could you help me use an extra code for two hands?