Save perspectives in view navigator

Summary:
Build upon D586 / T28819

(only 12bea1c9ada860a4b4f34ebeed67f61cece1ab3f is relevant)

Enable saving perspectives

Saving a modified perspective overwrites
the currently active perspective.

Test Plan:

1. open MITK workbench, open the ViewNavigator
2. double click on a view tree item to open another view
3. right-click on the current perspective and save the modified perspective
4. double click on a view tree item to open another view
5. right-click on the current perspective and reset the perspective
6. see how the latest view is removed and the saved, modified perspective is re-created
7. right-click on a tree item and close all perspectives
8. open the perspective again using the top menu
9. see how the modified perspective is re-created

Reviewers: kislinsk, O1 MITK Reviewer Group I, O3 MITK Reviewer Group II

Reviewed By: kislinsk, O1 MITK Reviewer Group I, O3 MITK Reviewer Group II

Subscribers: kislinsk, kalali

Maniphest Tasks: T26961

Differential Revision: https://phabricator.mitk.org/D588