Quite often the user wants to experiment what particular unit(s) add
to the sound. This commit adds ability to disable any set of units
temporarily, without actually deleting them. Ctrl-D disables and
re-enables the units. Disabled units are considered non-existent in
the patch.
Closes#116.
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.
