ProjectExplorer: Handle parsingStarted/Finished in BuildConfiguration

Make all buildconfigurations disabled while the project parses.

This unifies how this is handled in different build systems.

Change-Id: I6afca3743ad1433529a4f9d3bfdf73042799e456
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/qbsprojectmanager/qbsproject.cpp

@@ -410,11 +410,6 @@ QString QbsProject::profileForTarget(const Target *t) const
     return QbsManager::profileForKit(t->kit());
 }
 
-bool QbsProject::hasParseResult() const
-{
-    return qbsProject().isValid();
-}
-
 qbs::Project QbsProject::qbsProject() const
 {
     return m_qbsProject;