improve error handling for loading config file

[ivinjabraham]

Prerequisite

This change assume we can change App::new() to initialize logging earlier, since currently it is only initialized after Config is built as seen here:

    pub fn new() -> App {
        let config: Config = Config::build();
        config.create_dirs();

        ...

        // Initialize the logger before the app starts
        Logger::init_log_file(&config);
        Logger::info("patch-hub started");
        logging::garbage_collector::collect_garbage(&config);

And it seems #99 should allow us to do so.

Overview of changes

Previously, errors when failing to read or parse the config. file were not logged. Errors in failing to read was also silently mitigated by defaulting to an empty string, which could lead to more problems down the road.

Users are still not notified directly (they will have to check the logs) when this happens, and I think that might be necessary?