"Delete All" on the reclaim dialog should not delete hdiso source (#980496).
    
    Lots of little pieces to make this one go:
    
    (1) Don't call recursiveDelete on disks.  That's what actually causes the
    traceback in the bug report.
    
    (2) Change IMMUTABLE_COL to TYPE_COL so we have a way of telling what's
    protected, what's the free space line, etc.
    
    (3) Decide whether the user's asked to reclaim anything by counting up
    delete actions, not by size.  This lets us take existing free space into
    account.
    
    (4) Give existing free space lines in the store an empty action so
    everywhere we do something based on action, those won't be touched.
    
    (5) Stop basing action visibility on whether a device is editable or not.
    Always show them, which is why #4 is needed.