Adding dynamic USB power support

- Each scan module now has a current change callback which passes the available current as a parameter
- No longer attempts to use the max 500 mA immediately, starts with 100 mA then goes to 500 mA after enumeration
- If enumeration fails due to bMaxPower of 500 mA, then attempt again at 100 mA (might also be possible to go even lower to 20 mA in certain cases)
- Now working with the Apple Ipad (no over-power messages)
- Fixed Wake-up behaviour on Apple Ipad (and likely other iOS devices)
- More effecient set_feature/clear_feature handling (device handler)
- Initial power handling via Interconnect (still needs work to get it more dynamic)

Scan/PortSwap/port_scan.h

@@ -1,4 +1,4 @@
-/* Copyright (C) 2015 by Jacob Alexander
+/* Copyright (C) 2015-2016 by Jacob Alexander
  *
  * This file is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -28,3 +28,5 @@
 void Port_setup();
 uint8_t Port_scan();
 
+void Port_currentChange( unsigned int current ); // Called by Output Module
+