Feature/embedded subtitles

[gtsteffaniak]

Description

Includes the core functionality of #1072

With the following changes:

1. integrates subtitles with content into resources api when content=true
2. removes ping-pong api requests when viewing files in the ui. instead of api requests for each track, they all exist on the same api request response on resource
3. adds caching so ffmpeg is not called multiple times for the same content when a video is opening by several people or the same person multilple times (24 hours or on file modtime change)
4. reorganizes ffmpeg commands into ffmpeg package for consistency.

Additional Details

fyi @maxbin123 maxbin123