A template set can now obtain a template by calling the function
getTemplate (if any) received in the initial config.
The returned value can be an Element instance, a template string, a
function (i.e. a compiled template), or null. In the last case, owl will
look into the template set rawTemplates object.
This commit adds a warning when an async hook
(onWillUpdateProps/onWillStart) takes longer than 3 seconds, as these
hooks block the rendering and patching of the application, it is rarely
desirable and often a sign of a deadlock. This warning will contain the
stack trace of the call to the hook to help in debugging.
Mathieu Duckerts-Antoine