Make the graph scalable by adjusting the painting code of the envelope so that it does not assume fixed widths and heights anymore. Remove the setting of a fixed size from the envelope graph and only set a minimum size.
Make three scaling modes available which can be selected via a context menu in the graph:
* "Dynamic": This modes corresponds to the rendering strategy of the previous implementation. Initially 80/182 of the available width is used as the maximum width per segment. This can be interpreted like a "zoomed" version of the absolute mode. If the needed space becomes larger than the full width though then it falls back to relative rendering.
* "Absolute": Each of the five segments is assigned 1/5 of the available width. The envelopes will always fit but might appear small depending of the current settings. This is a good mode to compare envelopes though.
* "Relative": If there is at least one non-zero segment then the whole width is always used to present the envelope.
The default scaling mode is "Dynamic".
## Technical details
The new painting code is more or less divided into two parts. The first part calculates `QPointF` instances for the different points. In the second part these points are then used to draw the lines and markers. This makes the actual rendering code much more straight forward, readable and maintainable.
The interpolation between the line color of an inactive and an active envelope has also been restructured so that it is much more obvious that we are doing an interpolation in the first place. The colors at both ends of the interpolation are explicit now and can therefore be adjusted much easier. The actual color interpolation is done in the helper function `interpolateInRgb` which is provided by the new class `ColorHelper`. This class will later also be needed when the LFO graph is made scalable.
The line is rendered as a polyline instead of single line segments.
The drawing of the markers has been abstracted into a lambda (with some outside captures though) so that it can be easily adjusted if necessary. The markers are rendered as circles instead of rectangles because that looks much nicer especially when the widget is rendered at a larger size.
The width of the lines and marker outlines is determined using the size of the widget so that it scales with the size.
A `lerp` function has been added to `lmms_math.h`.
Move the envelope and LFO graphs into their own classes.
Besides the improved code organization this step had to be done to be able to use layouts in `EnvelopeAndLfoView`. The class previously had fixed layouts mixed with custom rendering in the paint event. Mouse events are now also handled in both new classes instead of in `EnvelopeAndLfoView`.
## Layouts in EnvelopeAndLfoView
Use layouts to align the elements of the `EnvelopeAndLfoView`. This removes lots of hard-coded values. Add helper lambdas for the repeated creation of `Knob` and `PixmapButton` instances.
The spacing that is explicitly introduced between the envelope and LFO should be removed once there is a more open layout.
## Layouts for InstrumentSoundShapingView
Use layouts to align the elements of the `InstrumentSoundShapingView`.
## Info text improvements in LFO graph
Draw the info text at around 20% of the LFO graph's height. This prepares the dialog to be scaled later.
Write "1000 ms/LFO" instead of "ms/LFO: 1000" with a larger gap.
## Accessors for EnvelopeAndLfoParameters
Make the enum `LfoShape` in `EnvelopeAndLfoParameters` public so that it can be used without friend declarations. Add accessor methods for the model of the LFO.
## Other improvements
* Adjust include orders
* Variable initialization in headers
* Prevention of most vexing parses
