* Make device_creator a variable template and get rid of the ampersands
* Remove screen.h and speaker.h from emu.h and add where necessary
* Centralise instantiations of screen and speaker finder templates
* Add/standardise #include guards in many hearers
* Remove many redundant #includes
* Order #includesr to help catch headers that can't be #included alone
(nw) This changes #include order to be prefix, unit header if applicable
then other stuff roughly in order from most dependent to least dependent
library. This helps catch headers that don't #include things that they
use.
6c23897483