refactor: migrate from mod.rs to named module files

src/system/mod.rs

@@ -1,15 +0,0 @@
-//! ## System
-//!
-//! `system` is the module which contains functions and data types related to current system
-
-// modules
-pub mod auto_update;
-pub mod bookmarks_client;
-pub mod config_client;
-pub mod environment;
-mod keys;
-pub mod logging;
-pub mod notifications;
-pub mod sshkey_storage;
-pub mod theme_provider;
-pub mod watcher;