Fixed some memory leaks. Manipulation of namespaces: set, remove, replace, normalize. Manipulation of prefixes: set, remove, replace. Fix #37 (https://github.com/lbellonda/qxmledit/issues/37). Autocompletion editing attributes (activated with ctrl+space). Added error message in splitting files operation. New options for splitting files: extract and group, even in CSV format. Fixed a bug on schema choose dialog.