Improve the removal of entities with dependencies

[jonasraoni]

Describe the bug
When the user attempts to remove an entity that has dependencies (e.g. merge it with another), such as a section, the user is blocked from doing so, until he clears manually all of those dependencies. That's tough for the user, and if the dependency spans across several tables, it's kind of unfeasible to do it manually.

We can simplify the user life with some improvements/bulk actions:

• Display the list of dependencies
• Offer generic actions:
  • Clear the dependencies (when possible, by assigning null)
  • Remove the dependencies (under a confirmation)
  • Re-assign to another record

What application are you using?
OJS 3.4