[Maintainer] Add a simple way to replace Soundtracks

[0lhi]

Is your feature request related to a problem? Please describe.
While there is a quick and convenient way to convert MP3s into OGGs, there is none for replacing them with SPCs.

Describe the solution you'd like
Add a "Replace Soundtrack" option that lists every music file of an Episode, have the user select one, and replace all instances of it in the episode with any compatible file that the user chooses.

Describe alternatives you've considered
Years ago I used a command that replaces all mentions of "music.mp3" in Level files with "music.ogg". It worked, but it was inconvenient.

Additional context
Would make it tremendously easier to create Repacks of Episodes.

[Wohlstand]

I do keep this idea too, because I do produce several episode repaks too where I do replace musics. Even there are sort of remixes where I completely replace given music with a new one. Good idea! 🦊 👍

[0lhi]

Did a drawing of how I imagine it:

Files in Subfolders should be displayed as Music/Song.mp3 or LevelFolder/Song.mp3.

Maybe an Output field could be added, too, that shows what files have been edited.

[Wohlstand]

In order to prepare to implement this feature, I made a small re-organising: I made the shared library of Qt-based modules and dialogues that I will share between many modules (Editor and Maintainer primarily), including translations (to stop forcing our translators to do the double work on the same module shared between two or more components).

[Wohlstand]

Moved to the NEO milestone.