Change the short cut and icon for register 'Blank'

Change the short cut from CTRL+Page_Down to CTRL+b and change the
toolbar icon to 'go-jump'.

gnucash/ui/gnc-plugin-page-register.ui

@@ -268,7 +268,7 @@
     <item>
       <attribute name="label" translatable="yes">_Blank Transaction</attribute>
       <attribute name="action">GncPluginPageRegisterActions.BlankTransactionAction</attribute>
-      <attribute name="accel">&lt;Primary&gt;Page_Down</attribute>
+      <attribute name="accel">&lt;Primary&gt;b</attribute>
       <attribute name="tooltip" translatable="yes">Move to the blank transaction at the bottom of the register</attribute>
       <attribute name="temp" translatable="no">yes</attribute>
     </item>
@@ -613,7 +613,7 @@
         <property name="action-name">GncPluginPageRegisterActions.BlankTransactionAction</property>
         <property name="tooltip-text" translatable="yes">Move to the blank transaction at the bottom of the register</property>
         <property name="use-underline">True</property>
-        <property name="icon-name">go-bottom</property>
+        <property name="icon-name">go-jump</property>
       </object>
       <packing>
         <property name="expand">False</property>