Added option for local Hydra instance for file serving and videos are not restarted on re-runs

[MaikSteiger]

I have made two commits, one targeting the possibility of using local files from your machine in the video synthesizer directly, rather than providing a URL to a remote resource. The second one just handles code re-runs on video sources, such that they are not reinitialized to play from frame=0 for each re-run, but it just continuously plays for a better live coding experience.

For the local files, it will mostly be useful for local instances running Hydra via npm run dev. For that use case I have introduced a new constant in the code editor F that directly points to the URL serving the files.

Example:
I want to use a video file called foo.mp4 as source for my project. I would just drag and drop that file into the files directory in the Hydra Repository and load it via:

// More general syntax
s0.initVideo(F + "foo.mp4")

// Or use string concatenation
s0.initVideo(`${F}foo.mp4`)