Previously images that could not be located were handled by throwing a
full report error, which incorrectly stated it was an invalid image
*type*.
This changes the image handling to instead log a single-line warning
directly in the image provider code, reducing the error handling
required by each consumer.
Resolves#146.
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.
