Make BuildSteps one instance per BuildConfiguration

Enables users to change which buildsteps get run per buildconfiguration.
Some further tweaks are probably necessary. This is a rather big
change, though it should work. :)

src/plugins/genericprojectmanager/genericproject.h

@@ -103,7 +103,6 @@ public:
     virtual QStringList files(FilesMode fileMode) const;
 
     QStringList targets() const;
-    GenericMakeStep *makeStep() const;
     QString buildParser(ProjectExplorer::BuildConfiguration *configuration) const;
     ProjectExplorer::ToolChain *toolChain() const;