Clear recording in a more advanced way

[pdawyndt]

As soon as any change is made to the blocks, the entire recording is cleared. We might make this smarter by either not clearing the recording altogether or not clearing the entire recording.

Some actions should not trigger clearing the recording, because they do not actually change the (behavior) of the code or the part of the code that has been executed so far:

• clean up block or manually dragging scripts to another location
• adding/removing "pause" blocks
• blocks added to, removed from or modified in a script that has not yet been executed
• blocks added to, removed from or modified in a section of a script that has not yet been executed

Even when blocks aadded to, removed from or modified in a (section of a) script that has already been executed, we may only clear the recording up to the point where the added/removed block would start changing the execution of the code. This is the first point in the recording where the previous block was executed.