feat(config): use default fallback with config instructions

When no config file is found, the bar will now automatically instead load a hard-coded default consisting of the `focused` and `clock` modules, and a `label` informing you the bar is not configured. Instructions are also printed to the log.

src/modules/clock.rs

@@ -34,6 +34,17 @@ pub struct ClockModule {
     pub common: Option<CommonConfig>,
 }
 
+impl Default for ClockModule {
+    fn default() -> Self {
+        ClockModule {
+            format: default_format(),
+            format_popup: default_popup_format(),
+            locale: default_locale(),
+            common: Some(CommonConfig::default()),
+        }
+    }
+}
+
 fn default_format() -> String {
     String::from("%d/%m/%Y %H:%M")
 }