Scroll trigger

[alexanderkirtzel]

Is your feature request related to a problem? Please describe.
Add a scroll trigger that fires after the page got scrolled to a specific threshold.

Describe the solution you'd like
Like load & click etc. the new trigger should be called scroll and needs a parameter about how deep a user should scroll to fire. E.g. elb-action=scroll(y). y could be percentage or absolute pixels where percentage would be the default value.

Additional context
Trigger parameters could be useful for others (see #7). Maybe there is a function from action filter that could be used.

[deepskydata]

That would be great