Improve DynamicAppConfigTrait
Improve DynamicAppConfigTrait

Changes:
- Add `setDynamicConfig()` for attaching a pre-built instance
- Add `loadDynamicConfig()` to create an instance from the pre-defined config class
- Modify `dynamicConfig()` to store a single new instance / return existing instance
- Throw an exception when swapping configset in `setAppConfig()` or `setDynamicConfig()`
- Fix `setAppConfig()` assinging undefined variables

mcaskill/charcoal-support,mcaskill/charcoal-support