This commit makes all errors thrown in owl use a custom error class. The
main point of this is to always wrap user-code errors that happen during
the owl lifecycle so that they can be treated uniformly in onError by
checking the cause property, and also allows user code to differenciate
owl errors from non-owl errors reliably at runtime.
This commit add supports for value types in prop validation. To describe
a value V type, one has to simply write {value: V}.
Note that this commit also improves the validation typing.
closes#1198closes#910