Includes: Cleanup around net main and wallet

-Move from .h to .cpp: in main, net and wallet
-Remove unnecessary #include "main.h"
-Cleanup some wallet files includes

src/qt/coincontroldialog.cpp

@@ -15,7 +15,7 @@
 
 #include "coincontrol.h"
 #include "init.h"
-#include "main.h"
+#include "main.h" // For minRelayTxFee
 #include "wallet/wallet.h"
 
 #include <boost/assign/list_of.hpp> // for 'map_list_of()'