Properly set up time cutting in the live camera mode

[BergmuellerNiklas]

Users are supposed to cut the in-app recorded video such that only the ROM analysis part is included. However, the video that gets submitted to the analysis is always the whole video.

This is a problem, since users will always get wrong values if they do not cut the video.

[lgerhardt45]

This is more advanced than expected but this SO answer has the solution: https://stackoverflow.com/a/55620798 with DispatchQueue stuff and this one sync: https://stackoverflow.com/a/35546955