osxbundle: add header padding to the binary

This avoids install_name_tool to run out of header space when changing the
paths to the dylibs.
input: enqueue commands to the end of the queue

`mp_input_queue_cmd` erroneusly added commands to the head of the queue
resulting in LIFO behaviour instead of the intended FIFO.
osxbundle: cocoa_common: change playlist on fileopen events

When opening new files in Finder when `mpv` is running from an application
bundle, the new files will now replace the current playlist.

Fixes #14