feat(settings): new settings migration utility for evolutions

[NPavie]

Introducing a setting migrator to allow safer changes of settings across versions when changes are required
(like merging or splitting settings)

A first migrator is provided to migrate current settings to a new version, including :

• merging the action setting for jobs and app on closing the main window (see Merge the two settings related to window closing #129)
• Adding a new setting to control if a job edition should be done in place or in a new job page (to prepare Consider letting "Edit job" open a new tab #130)
• cleaning up pipeline instance properties stored in settings

[marisademeglio]

This will also be helpful for #169 and #170

[marisademeglio]

This is the first time I've tried the new merged settings and this is what I see for each option when there is a completed job open:

1. keep all jobs open...: closes the window and keeps the job via tray icon
2. close all jobs...: displays the "jobs will be removed" warning, then I say "proceed", then it closes the window and the job, and the tray icon is there but with no jobs
3. quit the application: quits the application
4. ask each time: asks each time

It makes sense and also it seems to have migrated my old setting correctly.