feat: module-level name and class options

BREAKING CHANGE: To allow for the `name` property, any widgets that were previously targeted by name should be targeted by class instead. This affects **all modules and all popups**, as well as several widgets inside modules. **This will break a lot of rules in your stylesheet**. To attempt to mitigate the damage, a migration script can be found [here](https://raw.githubusercontent.com/JakeStanger/ironbar/master/scripts/migrate-styles.sh) that should get you most of the way.

Resolves #75.

src/main.rs

@@ -7,6 +7,7 @@ mod config;
 mod desktop_file;
 mod dynamic_string;
 mod error;
+mod gtk_helpers;
 mod image;
 mod logging;
 mod macros;