[Lazarus] StringGrid: Fix cells that are editable?

[Jürgen Hestermann]

In a StringGrid is it possible to fix cells but still allow them to be editable (as in Excel)?
For example, when I set FixedCols and FixedRows to 2 then I cannot edit cells[0,0] or cells[1,1] anymore.
When set to 0 then rows and columns that should permanently be visible move out of view when
moving the cursor to the right or down.