Improve module load failure feedback

[dlamkins]

When a module fails to load due to composing issues, dependency issues, etc. very little is shown to the user outside of what is written to the logs. That means that pressing the enable button appears to do nothing.

If a module fails for one of the above on-load reasons (so before it has even successfully enabled), the module should mark itself invalid and display the issue within the UI.

This is mostly specific to the above mentioned issues when the assembly is first loaded or composed. Other issues, such as those during load, already indicate failures in the UI.