Rework clone event tool

[aavilesd]

Right now, events are cloned into the same category they belong. This arises two problems:

1. People without permission to create new events in a category can do so by cloning an event in which they have management rights. This is a security issue.
2. The manager of an event, unless he is not also manager of the category, can't move the event to another category. This forces the user to contact the manager of the category to perform the action.

The sensible functionality of the cloning should be asking the manager of the event where he wants to clone the event into, among the categories in which he has permission to create new events.