Implemented optimized stringtable parsing
Minor cleanups
Goodbye, modular DemoPacketParser

The entire abstraction model around IMessageParser was nice, but costly.
All handlers are now covered using fast netmessages. Parsing these messages
is simply useless overhead. If someone needs it because they're searching for
data in some message that isn't implemented, they can just define SLOW_PROTOBUF
and everything will work exactly like before this commit (just slower).

But normal builds where all you want to do is parse some demos don't need that.