history: add method to clear the model and the backends

clearAllBackends() only deletes the file, but does not reset the
model; the new clear() method does both.

Change-Id: I39f37276b650b9511d08d8bd4f7c7b52a33a142a
Tuleap: #925

src/categorizedhistorymodel.cpp

@@ -564,14 +564,20 @@ void CategorizedHistoryModel::collectionAddedCallback(CollectionInterface* backe
 ///Call all collections that support clearing
 bool CategorizedHistoryModel::clearAllCollections() const
 {
-   foreach (CollectionInterface* backend, collections()) { //TODO use the filter API
-      if (backend->supportedFeatures() & CollectionInterface::SupportedFeatures::CLEAR) {
+    foreach (CollectionInterface* backend, collections(CollectionInterface::SupportedFeatures::CLEAR)) {
         backend->clear();
     }
-   }
     return true;
 }
 
+///Delete all history and clear model
+void CategorizedHistoryModel::clear()
+{
+    beginResetModel();
+    clearAllCollections();
+    endResetModel();
+}
+
 bool CategorizedHistoryModel::addItemCallback(const Call* item)
 {
    d_ptr->add(const_cast<Call*>(item));

src/categorizedhistorymodel.h

@@ -74,6 +74,7 @@ public:
    void setHistoryLimited(bool isLimited);
    void setHistoryLimit(int numberOfDays);
    void setHistoryEnabled(bool isEnabled);
+   void clear();
 
    //Model implementation
    virtual bool          setData     ( const QModelIndex& index, const QVariant &value, int role   ) override;