Draft: John's latest updates to nproject-ui

Implements a number of updates that I think are needed to the current nproject-ui branch. Note that this version breaks the logic for updating the job model when new jobs are submitted. That function is put back in a separate branch john/cumulus-job-tracker that will be submitted in a separate MR.

This MR is marked as draft because it is not intended to be merged into master directly, but instead to be combined with Corey's nproject-ui branch

• Update jobsManifest::getField() to tolerate new/undefined keys
• Update qtJobsModel to use the JobsManifest for the rowCount() method.
• Marks the project modified when a job is added. I have since rethought this feature but don't want to go back and undo it yet. Instead, I think we should save the job manifest file when jobs are added. (Otherwise they are gone forever if modelbuilder crashes or the user closes without saving the project).
• Clear qtProjectRuntime when project is closed. An oversight that Ryan pointed out.