Draft: introduce preparse process

This merge request depends on type serialization module !2979 .

It introduce the preparse process code in vlc tree.
The main goal of the preparse process is to delegate preparse tasks of vlc medialibrary and playqueue to an external process.
This permit to mitigate crashes of vlc while parsing medias.

The communication between vlc process and preparse process is done via stdin for requests and stdout for the serialized parsing result.

TODO:

• handle attachment found event properly, required by the medialibrary metadataextractor module
• medias usin credentials can't be parsed using preparse process for the moment, credentials access are not shared between vlc and the preparse process (see this issue)]