[feature] mac os: use forward/backward media keys for extra short jumps

hi,

some of my friends often work on audio transcriptions. since mac os doesn't allow global hotkeys, i have created a custom vlc build where the media keys on the keyboard (forward / backward) trigger extra short jumps forward and backward respectively.

i'd like to add this into mainline, possibly with and advanced macosx interface option "[ ] use forward / backward for extra small jumps" within "apple remote and media keys". should i prepare a patch / merge request?