Configuration system (for element ranks and other things)

Submitted by Benjamin Gaignard

Description

Created attachment 187346
draft of implementation

The idea is to offer a way to customize element ranking without hacking/patch code.
I need that feature because some decoders (like h264) may request to autoplug a parser between them and the demuxer. Today ins't possible without hack parser code.

This could be done by modify the element rank before write it into cache registry.
Modifications are store in a file (in a humain readable format) and I add a gst tool, named gst-rank, to edit this file.

All comments/review/help is welcome

~~Patch 187346~~, "draft of implementation":
0001-add-element-ranking-customization-feature.patch