fix(tooltip): respect animation attribute

Previously, it was only possible to set animation to false with an empty
string or through global options.

I don't think attributes that don't expect strings should be using `attrs.$observe` as the interpolation just creates extra work.

I suggest to use watchers on the scope, which isn't any performance impact as the `attrs.$observe` uses a watcher behind the scenes, anyway.

The same thing can be said of the popUpDelay but these changes might break existing setups. Hence, I left that as a separate refactor commit that can be dropped from this pull request and left for later.