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
PDI-689 - Copy / paste of steps doesn't copy error handling information
[PDI-7374] PDI REST Client should not log a status 204 as an error.
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
Merge pull request #165 from hudak/PDI-10862

PDI-10862 - Synchronized stepListeners collection
Merge pull request #164 from stepanovdg/PDI-7374

[PDI-7374] PDI REST Client should not log a status 204 as an error.
Merge pull request #163 from pavel-sakun/PDI-689

PDI-689 - Copy / paste of steps doesn't copy error handling information
Merge remote-tracking branch 'upstream/master'