LibCore: Put all classes in the Core namespace and remove the leading C

I've been wanting to do this for a long time. It's time we start being
consistent about how this stuff works.

The new convention is:

- "LibFoo" is a userspace library that provides the "Foo" namespace.

That's it :^) This was pretty tedious to convert and I didn't even
start on LibGUI yet. But it's coming up next.

Servers/AudioServer/ASEventLoop.cpp

@@ -31,7 +31,7 @@
 #include <unistd.h>
 
 ASEventLoop::ASEventLoop()
-    : m_server(CLocalServer::construct())
+    : m_server(Core::LocalServer::construct())
 {
     bool ok = m_server->take_over_from_system_server();
     ASSERT(ok);