Joren has improved this, but the behavior was unexpected when the user did not
start in a cell that contained the string to replace.  This commits changes
it further that when the user hits Replace:

* in a cell that does not contain the string to replace, it jumps to the cell
  that contains it, replaces the string, and stays there

* in a cell that contains only one occurrence of the string to replace, it
  replaces it, and jumps to the next cell that contains such a string

* in a cell that contains multiple occurrences, it replaces it, but does not
  move the cursor (so that the further occurences in that cell can still be
  replaced)

This seems to be the most intuitive behavior.

Change-Id: If6c10069b8dff933a035780732a7d7b6e0740383