qml: Add plus big filled icon

Author: johnny9

qml/bitcoin_qml.qrc

@@ -127,6 +127,7 @@
         <file alias="network-dark">res/icons/network-dark.png</file>
         <file alias="network-light">res/icons/network-light.png</file>
         <file alias="plus">res/icons/plus.png</file>
+        <file alias="plus-big-filled">res/icons/plus-big-filled.png</file>
         <file alias="pending">res/icons/pending.png</file>
         <file alias="shutdown">res/icons/shutdown.png</file>
         <file alias="singlesig-wallet">res/icons/singlesig-wallet.png</file>