[FEATURE ADD] Update file search and validation functionality

[HunterAP23]

Describe the feature that is being tested/implemented
Update file searching/scanning functionality.

• Reference files
  • By default, should be stored in directory named reference that's located in the project root folder
  • Can be changed by the user either through a command line argument or through the GUI
  • Should scan for any files with the following extensions:
    • MP4
    • MKV
    • MOV
    • AVI
    • WEBM
    • TS
    • FLV
  • Should validate the files by doing an ffmpeg encode to nul with them like ffmpeg -i INPUT -f null -. Validated fiels are given a "validated" status in the completions file.
• Encoded files
  • By default, should be stored in directory named encoded that's located in the project root folder
  • Can be changed by the user either through a command line argument or through the GUI
  • Should contain a subdirectory for each reference file
• VMAF report files
  • By default, should be stored in directory named data that's located in the project root folder
  • Should contain a subdirectory for each reference file that stores each output VMAF report that is named after the encoded file it came from.
• VMAF score graph files
  • By default, should be stored in directory named graphs that's located in the project root folder
  • Can be changed by the user either through a command line argument or through the GUI
  • Should contain a subdirectory for each reference file that stores each output VMAF score graph that is named after the encoded file it came from.

List any relations to other issues in this repository or in other repositories
N/A