The exception to the rule is the dialog buttons (which use still
the default material buttons), because when there is a modal dialog
on screen, there is not much else the user would want to do.
Fixes#156
The Model was getting unmaintanable mess. This is an attempt to refactor/rewrite the Model so that data of certain type is exposed in standardized way, offering certain standard manipulations for that data type, and on the GUI side, certain standard widgets to tied to that data.
This rewrite closes#72, #106 and #120.
