Add/update preference screen icons

Defaults and language icons were missing, and graph/profile
icon was not readable.

All icons except "language.png" were taken from Google's
Material Design Icon pack which is distributed under Apache 2.0 license
(see https://github.com/google/material-design-icons)

Language icon is from http://languageicon.org site. If their
license isn't permissive enough, then we can switch to a language icon
from Material Design pack (globe).

Signed-off-by: Sergey Starosek <sergey.starosek@gmail.com>

subsurface.qrc

@@ -80,5 +80,7 @@
         <file alias="duringPhoto">icons/duringPhoto.png</file>
         <file alias="outsidePhoto">icons/outsidePhoto.png</file>
         <file alias="inAndOutPhoto">icons/inAndOutPhoto.png</file>
+        <file alias="language">icons/language.png</file>
+        <file alias="defaults">icons/defaults.png</file>
     </qresource>
 </RCC>