Allow to specify a variable type using a prefix on the variable name (int, bool, double) if omitted, defaults to stringvar.
Fix bug on get_variable method.
Merge branch 'master' into dev
Reduce initial window size to 640x480.
Check that preview was created before delete.
Set application changed when an item is deleted.
Set default values for layout properties when adding a widget.
Avoid creating empty "rows/columns" and "row/column" elements when saving to xml.
Clear preview when a new file is open.