Enabled disabling/enabling the recording at runtime

[OwenZonneveld]

Allows the ZED GStreamer to start & stop recordings at runtime.
This is done by passing parameters to the zedsrc.

The two relevant parameters are

• recording-status: gboolean
• recording-filename: GString

Current issues:

• If the filename is not set before trying to record there may be some issues as it will use an empty filepath.
• Probably not organized how you'd like.

I currently have a gstreamer pipeline that is working using these changes.