I don't see why we need to call ShutdownWiiRoot on InitializeWiiRoot.
Also, atexit? Really? Not only is this unnecessary, it will also cause
ShutdownWiiRoot to be called twice in rapid succession for no reason.
Shouldn't make any difference in practice because
both IsRecordingInput and IsNetPlayRunning should
be false if a temporary NAND isn't being set up,
but doing it this way is cleaner regardless.
Dolphin is able to generate one with all correct default settings, so
we don't need to ship with a pre-generated SYSCONF and worry about
syncing default settings.
Additionally, this commit changes SysConf to work with session SYSCONFs
so that Dolphin is able to generate a default one even for Movie/TAS.
Which SYSCONF needs to be touched is explicitly specified to avoid
confusion about which file SysConf is managing.
(Another notable change is that the Wii root functions are moved into
Core to prevent Common from depending on Core.)
