Pass chain and client variables where needed

This commit does not change behavior. All it does is pass new function
parameters.

It is easiest to review this change with:

    git log -p -n1 -U0 --word-diff-regex=.

src/init.h

@@ -10,8 +10,17 @@
 #include <string>
 #include <util/system.h>
 
-class CScheduler;
-class CWallet;
+namespace interfaces {
+class Chain;
+class ChainClient;
+} // namespace interfaces
+
+//! Pointers to interfaces used during init and destroyed on shutdown.
+struct InitInterfaces
+{
+    std::unique_ptr<interfaces::Chain> chain;
+    std::vector<std::unique_ptr<interfaces::ChainClient>> chain_clients;
+};
 
 namespace boost
 {
@@ -20,7 +29,7 @@ class thread_group;
 
 /** Interrupt threads */
 void Interrupt();
-void Shutdown();
+void Shutdown(InitInterfaces& interfaces);
 //!Initialize the logging infrastructure
 void InitLogging();
 //!Parameter interaction: change current parameters depending on various rules
@@ -54,7 +63,7 @@ bool AppInitLockDataDirectory();
  * @note This should only be done after daemonization. Call Shutdown() if this function fails.
  * @pre Parameters should be parsed and config file should be read, AppInitLockDataDirectory should have been called.
  */
-bool AppInitMain();
+bool AppInitMain(InitInterfaces& interfaces);
 
 /**
  * Setup the arguments for gArgs