Add the new class `BarModelEditor` which is intended to become a new way
to adjust values of float models.
Simplify the layout in `LadspaMatrixControlDialog` by removing some
nested layouts. Remove the "Parameters" column.
Adjust `LadspaMatrixControlView` to implement the following changes:
* Show the name of the control next to toggle buttons (`LedCheckBox`).
* Use the new `BarModelEditor` for integer and float types.
* SHow the name of the control next to time based parameters that use
`TempoSyncKnob`.
The names are shown so that the "Parameters" column can be removed.
Technical details
------------------
The class `LadspaMatrixControlDialog` now creates a widget that contains
the matrix layout with the controls. This widget is then added to a
scroll area. The layout is populated in the new method
`arrangeControls`.
Add some helper methods to `LadspaMatrixControlDialog` which retrieve
the `LadspaControls` instance and the number of channels.
Add the implementation of `BarModelEditor` to `src/gui/CMakeLists.txt`.
TODOs
------
Extract common code out of the `Knob` class so that it can be reused by
`BarModelEditor`.
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