Add an evaluation tool for the NP Migrator, to allow deciding if migration needs to be done or not

Knowing the current limitations of this migrator, there are situations in which the migration to nested spaces is not necessarily a good idea (because pages will be renamed, stuff can break).
However, not migrating existing pages to the follow the parent child hierarchy has 2 consequences:

• keeping these pages as terminal
• "breaking" the breadcrumbs of the existing pages, which will display a breadcrumb based on their storage location rather than their parent (previously set in the breadcrumb)

The first bullet is not the concern of this issue, however, for the second bullet, this "breaking" depends on the amount of pages which have a parent that is different from their location (the webhome of the space they were stored in).
So this new feature is about adding a "comparator" between the "storage tree" and the "breadcrumbs tree" on an existing wiki, before running the migrator, that would allow a user to evaluate whether they need / want to run the migrator.

This comparison can have multiple forms:

• actual trees - not very scalable
• showing pages that have a "storage parent" that is different from the "breadcrumbs parent", relative (only immediate parent) and absolute (whole path)
• other tool

Please note that examples are important, especially for cases where there are differences (e.g. only counting the pages that have different parents, even if interesting, is less valuable than actually showing those pages)