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.
Before this commit, the generated code for the component directive was
using the current context as the place to look for static informations
(such as the sub components). However, it is not entirely correct, since
the current context may be different than the current component (which
is easily accessed by using the this variable).
Also, while doing this, we fix some issues in the t-set directive, which
as calling lazy values with the wrong this.