Move rename infrastructure from Job to AbstractItem

Job has some fairly complex infrastructure for handling renames:

• the special textbox in configure.jelly
• the handling in doConfigSubmit, including ProjectNamingStrategy integration, Apply vs. Save logic (including the tricky JENKINS-17401 fix), and the redirect
• rename.jelly (and rename.properties)
• doDoRename, with more checks and redirects

Reimplementing all this in another item type (such as Folder) is rather painful, involving a lot of duplicated code and thus an inability to fix a bug once in one place—or pick a different implementation, such as using a JavaScript dialog like we now use for deletion and other actions requiring confirmation.

This code should be pulled up into AbstractItem for easy reuse, with some hooks for domain-specific validation (such as Job.isBuilding).