Kexi: fix creating new reports - load layouts only for opening, not creating

Original code worked only because results of operations was not checked.

• move layout loading code to loadSchemaObject() - it was not implemented before
• createWindowData() is now trivial
• add checks for failed parsing of layout xml
• don't store report name, this information is in KexiWindow's part item already

Differential Revision: https://phabricator.kde.org/D211