Make manipulator search configuration more intuitive

[campagnola]

Right now we have two config options tipHeight and tipSearchHeight that are confusing and have weird interactions. Let's replace these with something more straightforward like

• minSearchHeight - minimum distance above the slice surface when bringing pipettes in for search
• searchFocusOffset - Z-distance from pipette to focal plane in search mode (positive values to give the pipette extra room, prevent crashing into objective; negative values to make the pipette easier to find)

For backward compatibility, we can catch the old options and raise a super-helpful error message that provides the new parameters and values to use.