Ability to force a specific package version

As a Studio user, in the application definition screen:

• Once a package is selected, I can click on a "force version" button
• Clicking that button allows me to:
• => Select an existing version among a list of valid possibilities for the current target platform version. Ordering for the list: empty option first (see below), then versions ordered in descending order (latest versions first). Snapshots are at the end of the list, in descending order.
• => Choose an empty option to remove the specific version dependency (useful if one was already chosen)
• => Save
• => Cancel

When saving, the dependency is expressed towards this specific version.
When cancelling, no change is made.
If I select the empty option and save, the dependency is expressed as usual to the generic package.

If a dependency is expressed on a given version and I change the target platform version:

• A validation error is displayed if package is not valid for this version:

  Package [Package Title] [Package Version] is not available for this Nuxeo Platform version.

  Application definition does not upgrade / downgrade the version automatically.