Fix PE1674, PE1672, PE1671.
PE1674: Add appropriate Types constant to array of accepted types for the string converter
PE1672: When scheduling branches, if the branch schedules to an empty list of operations,
  do not collapse, and return null instead.  Test for null in the trigger branch qso appropriately.
PE1671: Arrange for the delete objects to omit the dropped/created index.

Also, more fixes on the ConnectionValuesManager around execution step display.