CConfigDB is no longer a singleton, and its members are no longer
static.
This makes it possible to have several instances of it, useful for
testing of if we ever want to have different config profiles.
Also updates hooks to delete themselves on destruction, to fit a more
natural RAII pattern. Long-lived objects must take care to destroy hooks
before ConfigDB is reset.
Differential Revision: https://code.wildfiregames.com/D3866
This was SVN commit r25326.