C++: Custom directory list for Switch Header/Source

Some projects use separate directories for sources and headers.

An example tree:
*
|-- src
     |-- foo.cpp
|-- include
     |-- foo.h

Allow the user to specify directories for finding out-of-project related
header/source files, in addition to current directory

Task-number: QTCREATORBUG-8883
Change-Id: I57215c8f2feffcc246d0d161798290861bcfcdd4
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/cpptools/cppfilesettingspage.h

@@ -50,7 +50,9 @@ struct CppFileSettings
     CppFileSettings();
 
     QString headerSuffix;
+    QStringList headerSearchPaths;
     QString sourceSuffix;
+    QStringList sourceSearchPaths;
     bool lowerCaseFiles;
     QString licenseTemplatePath;