[WIP] Add oudep dependency download center

[EX3exp]

TODO:

• implement (dependency) download center for all oudep dependencies, (like in UVR & SynthV)
• Currently this is called as "download center", but if there are better name, please write a comment. 👀
• In final, it should open download center automatically when OU lacks specific dependency (by using exception handling), so user can select and download dependencies with ease.

1. Should have these features:

• Can show "all available dependencies' list" to user.
• Can show status of "which dependencies are installed (or not)", like (nsf_hifigan--Uninstalled --[info]--[download]).
  Download buttons of "already installed dependency" should be blocked, so user cannot click them.
• When user clicks specific dependency's download button, It should confirm to user by message window, like "Will you download dependency XXX?(total: XXMb)".
• Can show downloaded status, like (50% -- 50Mb/ 100Mb). (showing progress bar will be great for user experience)
• Can perform more than one download at once, also OU's other process should not be blocked while downloading. (should use async process.)

• Can categorize dependencies, like "Diffsinger / Vogen / ENUNU... etc." (will use combobox)

2. It Will use download center.yaml for management.

• So exactly what download center perform is :
  • Print dependencies' informations in download center.yaml into user view
  • Connect download link(in download center.yaml) with each dependency's download button.

3.download center.yaml should contain:

• oudep's name (like "nsf_hifigan")
• oudep's category (like "diffsinger")
• oudep's brief information (like "use when rendering diffsinger's voice...blahblah")
• oudep's file size(Mb) (like 10Mb)
• oudep's version (like 1.0.0)
• oudep's direct download link (github, google drive... anything.)