move most explicit getters in optionsmodel to header

- is more consistent and saves quite some lines of code

src/qt/optionsmodel.h

@@ -44,10 +44,10 @@ public:
 
     /* Explicit getters */
     qint64 getTransactionFee();
-    bool getMinimizeToTray();
-    bool getMinimizeOnClose();
-    int getDisplayUnit();
-    bool getDisplayAddresses();
+    bool getMinimizeToTray() { return fMinimizeToTray; }
+    bool getMinimizeOnClose() { return fMinimizeOnClose; }
+    int getDisplayUnit() { return nDisplayUnit; }
+    bool getDisplayAddresses() { return bDisplayAddresses; }
     QString getLanguage() { return language; }
 
 private: