Add support for default data provider policies

[prioux]

Currently, an admin can configure a data provider with limits as to which other data providers it can copy files to, and which portals/bourreaux the data can be synced to.

This shows up as a large array of checkboxes, in the data provider 'show' page, one checkbox per other data provider and per portal/bourreau. It's very cumbersome when there are hundred of data providers and the admin want to disable copying to all of them, for instance. All these checkboxes are stored in ugly metadata on the DP.

A data provider should have a few 'main' flags that control the default behavior to all DPs, and the user interface for selecting other DPs for exclusion/inclusion be chnaged to make it more convenient.