UI: sheet design: Excel compatibility: handling of conditional formatting not...

Followup to #643 - a very useful feature in sheet design / redesign is the automatic adaption of references to other cells. They are - mostly - created new for copies while adapted on move of cells. This provides the flexibility to change the layout while the logical and calculating structure is kept intact. Alas that works less good for conditional formats than for formulas. The attached sheet [testing_referencing.gnumeric](/uploads/87db4c06ea9ef8195821c08fd36828e4/testing_referencing.gnumeric) demonstrates most of the differences I found. It is not 'only' a UI / convenience issue, but also concerns compatibility and migration from other spreadsheets. While LO Calc maintains somewhat less and somewhat different but basically similar idiosyncrasies, Excel ( short check with '2010' ) seems to successfully handle conditional formatting the same way as formula references. Only exception: References to outside the sheet become #REF! for formulas while conditional formattings 'wrap'. There are some old bugs touching this problem, see list in 'Details' below, they are mostly handling slowdowns or crashes which I assume based on the same root / concept.

Details and possibly related - Click to expand

While not the same issue: conditional formatting is the most brutal / most effective thing I know to slow gnumeric, constructing a small area of cells with 'checkerboard' different conditional formatting and copying it to a large area likes to stall. While not reproducible and not 'stable' in file save: I experience rare but there are crashes related to conditional formats, mostly on copying / moving and undo by ctrl-z. Issues possibly related: #691: performance: conditional formats problematic, #643: conditional formatting sometimes loosing references, #597: Crash while copying and pasting a range of cells, possibly involving conditional formating and formula, #582: conditional formatting incorrect for relative references, #547: conditional formatting recalculation, #520: Conditional format ods problem, #406: Conditional Styles Over Clipboard, #361: Crash on conditional formatting, #350: Segfault on Copy Style in conditional formatting, #343: Crash on Copy in conditional formatting, #339: Crash when copying conditional formatting rule, #243: conditional formatting feature: hide row /column, #229: Slowness with very large area of conditional formatting,