ProjectConfiguration: Add isActive() method

Returns true if the ProjectConfiguration element is currently active
and false otherwise.

Just a convenience method.

Change-Id: If75809ae7e78149d264deaaf6adc4ca8a8be43c2
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/projectexplorer/buildconfiguration.cpp

@@ -323,6 +323,11 @@ QString BuildConfiguration::buildTypeName(BuildConfiguration::BuildType type)
     }
 }
 
+bool BuildConfiguration::isActive() const
+{
+    return target()->isActive() && target()->activeBuildConfiguration() == this;
+}
+
 ///
 // IBuildConfigurationFactory
 ///