When changing configuration in parallel by editing the configuration
file and calling the API, the server could get into a deadlock that
prevented any further action. This is fixed.
Path names are used as part of paths in several components: in the
recorder, in the playback server and in every HTTP-based component
(WebRTC, HLS, API). Special characters that allow to escape from the
intended directory are now forbidden in order to prevent directory
traversal attacks.
