Manually add ffmpeg and ffprobe

[whyboris]

😓 worse in some ways, but allows for manually choosing which version of FFmpeg to include 🤔

Currently Mac builds are broken with this -- because Mac complains about the security of executing a file that's already part of the build package

And build sizes are double of what they were before 😓 -- so probably not worth merging this in (unless I figure out how to bundle things better) 😓

[whyboris]

This may solve #933 🚀

If available, I can include FFmpeg that has hardware acceleration - creating a separate release just for nvidia cards 🤔

[whyboris]

Ran a bunch of tests, looks like -hwaccel cuda doesn't speed up, but instead slows down the extraction process 🤦‍♂️

So for now, I intend to use regular FFmpeg without cuda support 👌

This PR can still merge - as it may be nice to allow manual selection of FFmpeg without having to rely on an auto-downloader 🤔

[whyboris]

If I find time I will try to build FFmpeg from source with the --disable-encoders flag -- since VHA only needs to decode (will need to check if this stripped down FFmpeg can still write a jpg).

If it works out, I can have VHA's build be much smaller 🚀

Currently eager to release 3.3.0 so this will have to wait for another release 🙆‍♂️

[whyboris]

Couldn't build version 3.3.0 on a Mac for a while

Turned out I could use process.resourcesPath string that gets added via Electron

Using this branch: mac-ffmpeg 🚀 see the PR #990