* Add `Object:{is_class_of,is_extended_by}` to check inverse relationships
* Make tab scrolling more flexible
This adds tab scrolling commands and connects them to mouse scroll
events.
This way scrolling behavior can be customized more easily.
For example an alternative behavior could be:
```lua
keymap.add({
["wheelup"] = "root:switch-to-hovered-previous-tab",
["wheeldown"] = "root:switch-to-hovered-next-tab"
})
```
When a command is performed with parameters, those are now passed to the
predicate.
The predicate can then return, after the validity boolean, any other
value that will then be passed to the actual command.
If the predicate only returns the validity boolean, the original
parameters are passed through to the actual command.
This allows predicates to manipulate the received parameters, and allows
them to pass the result of an expensive computation to the actual
command, which won't have to recalculate it.
String and table predicates will now also return `core.active_view`.
Before the fix navigation between nodes in the root
view was broken: the scale factor wasn't taken into
account. Switching in the right and down directions
was impossible for scale factors greater than one.