Before this commit, Owl template compiler would handle readonly
attribute as readonly properties. But this is incorrect, since the
property is actually named readOnly.
With this commit, we make sure that readonly AND readOnly are both
interpreted as the `readOnly` property. This is due to the fact that
QWeb does not discriminate between attribute and properties, so we have
to infer which is which.
closes#1362
Before this commit, properties were just handled as a special case of
attributes. But it does not make that much sense, since they are
different. For example, the `readOnly` property does not have the same
name as the `readonly` attribute. The confusion probably comes from the
fact that QWeb does not distinguish between property and attributes, so
Owl has to infer which one is which.
With this commit, we introduce a `block-property` directive in blockdom,
and change the compiler to use it in emitted code. It has the additional
benefits of slightly shrinking the runtime code, since the `isProp`
function can now be located in the compiler.