Added IntelliJ IDEA color scheme

It's missing some highlights that we currently don't support, but it
comes very close.

share/qtcreator/styles/grayscale.xml

@@ -30,6 +30,8 @@
   Selection
   Occurrences
   Occurrences.Rename
+  Occurrences.Unused
+  VisualWhitespace
 
   -->
 </style-scheme>

share/qtcreator/styles/intellij.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<style-scheme version="1.0" name="IntelliJ IDEA">
+  <style name="AddedLine" foreground="#00aa00"/>
+  <style name="Comment" foreground="#808080" italic="true"/>
+  <style name="CurrentLine" foreground="#000000" background="#ffffd7"/>
+  <style name="DiffFile" foreground="#000080"/>
+  <style name="DiffLocation" foreground="#0000ff"/>
+  <style name="Doxygen.Comment" foreground="#808080" italic="true"/>
+  <style name="Doxygen.Tag" foreground="#808080" bold="true" italic="true"/>
+  <style name="Field" foreground="#660e7a" bold="true"/>
+  <style name="Keyword" foreground="#000080" bold="true"/>
+  <style name="Label" foreground="#800000" bold="true"/>
+  <style name="Local" foreground="#000000"/>
+  <style name="Number" foreground="#0000ff"/>
+  <style name="Operator" foreground="#000000"/>
+  <style name="Parentheses" foreground="#ff0000" background="#c3e1ff"/>
+  <style name="Preprocessor" foreground="#000080" bold="true"/>
+  <style name="RemovedLine" foreground="#ff0000"/>
+  <style name="String" foreground="#008000" bold="true"/>
+  <style name="Text" foreground="#000000" background="#ffffff"/>
+  <style name="Type" foreground="#000000"/>
+  <!--
+  Relying on default colors for:
+
+  CurrentLineNumber
+  DisabledCode
+  LineNumber
+  Link
+  SearchResult
+  SearchScope
+  Selection
+  Occurrences
+  Occurrences.Rename
+  Occurrences.Unused
+  VisualWhitespace
+
+  -->
+</style-scheme>