Fix broken tags in Slovenian help translation
ruler: Seeks need to be on idle to compress the seeks while scrubbing
utils/pipeline: Save the position of the last compressed seek

This ensures we actually seek to the correct position, the one requested last.
Put multiple new clips in sequence on the same layer

Earlier the code would put all clips on top of each other and give each
clip its own layer. This is unexpected and not very helpful.
timeline: Move some docstrings to be inside the methods they refer to
utils/timeline: Provide context to a comment with a protected historical status
timeline: Clarify the scrollToPosition code and add programming safeguards

If out-of-bounds values are provided, warnings are emitted to aid debugging
timeline: Fix the "Zoom fit" and automatic scrolling behavior for clip insertion

- On drag and drop, call scrollToPosition with an X position, not nanoseconds;
  this prevents the timeline from scrolling to the end everytime.

- While inserting (multiple) clips, cache the value of zoom_fitted;
  this prevents repeated insertions from deactivating the fitted zoom

- Add a margin on the left of clips we scroll to during a drag & drop insert
- Simplify scrollToPlayhead's call to scrollToPosition
- Add more debugging statements