Move some static functions out of wallet.h/cpp

This commit just moves a few function declarations and updates callers.
Function bodies are moved in two followup MOVEONLY commits.

This change is desirable because wallet.h/cpp are monolithic and hard to
navigate, so pulling things out and grouping together pieces of related
functionality should improve the organization.

Another proximate motivation is the wallet process separation work in
https://github.com/bitcoin/bitcoin/pull/10973, where (at least initially)
parameter parsing and fee estimation are still done in the main process rather
than the wallet process, and having functions that run in different processes
scrambled up throughout wallet.cpp is unnecessarily confusing.

src/init.cpp

@@ -43,6 +43,7 @@
 #include "utilmoneystr.h"
 #include "validationinterface.h"
 #ifdef ENABLE_WALLET
+#include "wallet/init.h"
 #include "wallet/wallet.h"
 #endif
 #include "warnings.h"
@@ -420,7 +421,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-maxuploadtarget=<n>", strprintf(_("Tries to keep outbound traffic under the given target (in MiB per 24h), 0 = no limit (default: %d)"), DEFAULT_MAX_UPLOAD_TARGET));
 
 #ifdef ENABLE_WALLET
-    strUsage += CWallet::GetWalletHelpString(showDebug);
+    strUsage += GetWalletHelpString(showDebug);
 #endif
 
 #if ENABLE_ZMQ
@@ -1035,7 +1036,7 @@ bool AppInitParameterInteraction()
         if (!ParseMoney(gArgs.GetArg("-minrelaytxfee", ""), n)) {
             return InitError(AmountErrMsg("minrelaytxfee", gArgs.GetArg("-minrelaytxfee", "")));
         }
-        // High fee check is done afterward in CWallet::ParameterInteraction()
+        // High fee check is done afterward in WalletParameterInteraction()
         ::minRelayTxFee = CFeeRate(n);
     } else if (incrementalRelayFee > ::minRelayTxFee) {
         // Allow only setting incrementalRelayFee to control both
@@ -1068,7 +1069,7 @@ bool AppInitParameterInteraction()
     nBytesPerSigOp = gArgs.GetArg("-bytespersigop", nBytesPerSigOp);
 
 #ifdef ENABLE_WALLET
-    if (!CWallet::ParameterInteraction())
+    if (!WalletParameterInteraction())
         return false;
 #endif
 
@@ -1245,7 +1246,7 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
 
     // ********************************************************* Step 5: verify wallet database integrity
 #ifdef ENABLE_WALLET
-    if (!CWallet::Verify())
+    if (!WalletVerify())
         return false;
 #endif
     // ********************************************************* Step 6: network initialization
@@ -1566,7 +1567,7 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
 
     // ********************************************************* Step 8: load wallet
 #ifdef ENABLE_WALLET
-    if (!CWallet::InitLoadWallet())
+    if (!InitLoadWallet())
         return false;
 #else
     LogPrintf("No wallet support compiled in!\n");