Provide a "Partial failure" bootstrap mode in Weld SE

When booting weld, in the case of Seam Forge, a single bad plugin (beans archive) on the classpath, will cause boostrap to fail, and the entire system exits with failure.

What is desired is a "partial-failure" mode, where beans archives that fail to load can be "veto'd" or "excluded" from the live system, with a chance to print a friendly error message or take some kind of action on that failure, while all remaining "good" plugins/beans archives continue to load and boot as normal.

The only difference at runtime is that no beans from the failed archives are made available (of course, if this caused failure in an upstream beans archive, the system would have to fail that archive as well,) but in any case, if the beans archives that failed were "standalone" and did not break all archives' bean graphs, it should be possible to proceed to boot.

This would make error recovery in Forge much easier to handle, and also open up some interesting possibilities for other modular plugin-systems.