- ProvideNumericId: Allow explicit creation of Objects with Id 0.

- ProvideNumericId: Allow explicit creation of Objects with Id 0.
- Source: Make Source::noSource always have numericId 0 assigned.
- SourceManager:
  - Ignore attempt to add Source::noSource.
  - Fixed doc addSource/removeSource, they do not throw.
  - Removed addSource(url, ...) as Source creation is
    SourceFactory job. We don't want to maintain a duplicate
    SourceFactory interface here. And this way addSource does
    not throw anymore.