CLI: Add Import XML command (#3572)

The CLI now contains an "import" command that creates a new database from the specified XML export. The new database is in kdbx 4 format, and does not currently accept a keyfile in database creation.

This change is required to create new databases from XML backups.

Fixes #2458

src/core/Database.h

@@ -73,6 +73,7 @@ public:
     bool save(QString* error = nullptr, bool atomic = true, bool backup = false);
     bool save(const QString& filePath, QString* error = nullptr, bool atomic = true, bool backup = false);
     bool extract(QByteArray&, QString* error = nullptr);
+    bool import(const QString& xmlExportPath, QString* error = nullptr);
 
     bool isInitialized() const;
     void setInitialized(bool initialized);