Qt: HiDPI (retina) support for splash screen

- remove splash screen images (reduce binary size)
- dynamicly draw splash screen with available icon.
- remove testnet icon
- dynamicly colorize testnet icon

src/qt/bitcoin.qrc

@@ -25,7 +25,6 @@
         <file alias="editpaste">res/icons/editpaste.png</file>
         <file alias="editcopy">res/icons/editcopy.png</file>
         <file alias="add">res/icons/add.png</file>
-        <file alias="bitcoin_testnet">res/icons/bitcoin_testnet.png</file>
         <file alias="edit">res/icons/edit.png</file>
         <file alias="history">res/icons/history.png</file>
         <file alias="overview">res/icons/overview.png</file>
@@ -52,8 +51,6 @@
     </qresource>
     <qresource prefix="/images">
         <file alias="about">res/images/about.png</file>
-        <file alias="splash">res/images/splash.png</file>
-        <file alias="splash_testnet">res/images/splash_testnet.png</file>
     </qresource>
     <qresource prefix="/movies">
         <file alias="spinner-000">res/movies/spinner-000.png</file>