Improvement: Return JSON responses from core

[omeryusufyagci]

Currently the backend relies on parsing stdout to determine if the MediaProcessor was able process properly the requested media.

Add sendSuccessResponse(), and sendErrorResponse() to Utils, and ensure the status is propagated properly throughout.

Example:

if (!configManager.loadConfig("config.json")) {
    ResponseHandler::sendErrorResponse("Could not load configuration.");
    return 1;
}

This needs the corresponding backend code to be updated to ensure functionality. Will be merged together, from the dedicated branch opened here.

[DDibyajyot]

Hey, I'd love to work on this, could I get assigned this issue?