Rewite accout list model
The model of the account list should be re-worked.
Currently it is based on QStandardItemModel. This has several drawbacks:
- The data are stored twice -- in the model itself and in the global account container.
- Manipulating with model is cumbersome -- a lot of model elements have to be shuffled.
- Navigating in model and determining the user account is a pain.
The model should be rewritten using QAbstractItemModel:
- Only a structure related to the actual ordering would be held by the model.
- Model will provide data from the global account container (no data duplication).
- Some code from main window can be 'hidden' into the model.
Also, re-writing the model will probably make the treatment of issue #227 easier.