secret: Create virsecretobj.c and virsecretconf.h
    
    Move virSecretObj from secret_driver.c to virsecretobj.h
    
    To support being able to create a hashed secrets list, move the
    virSecretObj to virsecretobj.h so that the code can at least find
    the definition.
    
    This should be a temporary situation while the virsecretobj.c code
    is patched in order to support a hashed secret object while still
    having the linked list support in secret_driver.c. Eventually, the
    goal is to move the virSecretObj into virsecretobj.c, although it
    is notable that the existing model from which virSecretObj was
    derived has virDomainObj in src/conf/domain_conf.h and virNetworkObj
    in src/conf/network_conf.h, so virSecretObj wouldn't be unique if
    it were to remain in virsecretobj.h  Still adding accessors to fetch
    and store hashed object data will be the end goal.
    
    Add definitions and infrastucture in virsecretobj.c to create and
    handle a hashed virSecretObj and virSecretObjList including the class,
    object, lock setup, and disposal API's. Nothing will call these yet.
    
    This infrastructure will replace the forward linked list logic
    within the secret_driver, eventually.