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/net.h

@@ -8,7 +8,6 @@
 
 #include "bloom.h"
 #include "compat.h"
-#include "hash.h"
 #include "limitedmap.h"
 #include "mruset.h"
 #include "netbase.h"
@@ -17,7 +16,6 @@
 #include "streams.h"
 #include "sync.h"
 #include "uint256.h"
-#include "utilstrencodings.h"
 
 #include <deque>
 #include <stdint.h>
@@ -31,7 +29,6 @@
 #include <boost/signals2/signal.hpp>
 
 class CAddrMan;
-class CBlockIndex;
 class CScheduler;
 class CNode;