The purpose of this patch is to make file opening transparent. Changes:
1) no wild attaching and detaching storage

That was cause of a memory leak. Now a storage is created and attached only after successful opening of a file.

2) new KMyMoneyApp::Private::fileAction

It's central place for gathering all actions, app needs to undertake after a change in load state of a file.

3) user can choose to save newly created file as sql

Previously only xml was possible. Now user can even choose to not save it at all, which makes app independent from any storage plugin.

4) app doesn't crash if no storage plugin is loaded

5) no unnecessary update of actions which depend on load state of file

Differential Revision: https://phabricator.kde.org/D13408