Add a generic variable chooser widget.

The chooser allows choosing variables from a list, and inserting them
into previously focused line edit, text edit, or plain text edit.
Variables are now registered with a description in the variable manager.
Also make the QT_INSTALL_BINS --> CurrentProject:QT_INSTALL_BINS for
consistency.

src/plugins/coreplugin/variablemanager.cpp

@@ -63,6 +63,7 @@ class VariableManagerPrivate : public QObject
 public:
     QHash<QString, QString> m_map;
     VMMapExpander m_macroExpander;
+    QMap<QString, QString> m_descriptions;
     static VariableManager *m_instance;
 };
 
@@ -113,6 +114,21 @@ VariableManager* VariableManager::instance()
     return VariableManagerPrivate::m_instance;
 }
 
+void VariableManager::registerVariable(const QString &variable, const QString &description)
+{
+    d->m_descriptions.insert(variable, description);
+}
+
+QList<QString> VariableManager::variables() const
+{
+    return d->m_descriptions.keys();
+}
+
+QString VariableManager::variableDescription(const QString &variable) const
+{
+    return d->m_descriptions.value(variable);
+}
+
 } // namespace Core
 
 #include "variablemanager.moc"