PDI-10828 - Variables in Commit Size for Update, Insert/Update and Delete
Steps are not accepted

What was done:
1)changed Meta classes to support string value
2) changed step classes to convert string to value with respect to
variables
3) changed dialog classes to avoid unnecessary convertions
4) added unit tests
PDI-10828 - Variables in Commit Size for Update, Insert/Update and Delete
Steps are not accepted

UI changes to mark fields that they support variables
PDI-10828 - Variables in Commit Size for Update, Insert/Update and Delete Steps are not accepted

What was done:
1) changed the way bug is fixed according to Matt Burgess's notes
2) added backward compatibility support
Merge pull request #158 from kolinus/PDI-10828-2

Pdi 10828 - Variables in Commit Size for Update, Insert/Update and Delete Steps are not accepted