move most explicit getters in optionsmodel to header

- is more consistent and saves quite some lines of code

src/qt/optionsmodel.cpp

@@ -262,23 +262,3 @@ qint64 OptionsModel::getTransactionFee()
 {
     return nTransactionFee;
 }
-
-bool OptionsModel::getMinimizeToTray()
-{
-    return fMinimizeToTray;
-}
-
-bool OptionsModel::getMinimizeOnClose()
-{
-    return fMinimizeOnClose;
-}
-
-int OptionsModel::getDisplayUnit()
-{
-    return nDisplayUnit;
-}
-
-bool OptionsModel::getDisplayAddresses()
-{
-    return bDisplayAddresses;
-}