Major Refactoring and Introduction of a proper UI for the whole process alongside small QoL changes

[sudotman]

Major changes to the script are as follow:

• Changed the flow of the script from relying on public variables to be displayed to a flow that relies on OnGUI() and hence allows the ability to display custom text, fields with greater control over the window displayed too.
• Keeping in line with the change mentioned, also added a few helpful labels in between the fields. [also categorized them]
• The code is pretty tight already for the most part but still refactored the code a bit wherever I could.
• Added an extra legacy support line inside Secondary UV generation for versions older than 2022.
• Few QoL tweaks such as the automatic assignment of the currently selected object in the hierarchy as the Parent Object.
• Reflected these changes in the readme as such.

Thanks for the great script, hope these are helpful, cheers.