AutomatableModel: reset value to default if data is unavailable in loadSettings()

When loading older projects where a particular model did not exist and
thus did not save any data do not load the possibly invalid default data
but reset to default value of model.
Revert "Revert "Extensions for peak controller. Fulfills request 144.""

Now that we solved the problem with wrong default values in newly
introduced models when loading older projects we can safely implement
the new PeakController features.

This reverts commit 9cb52ccf0d84b31945b86cbf419db854c0d91204.
AutomatableModel: renamed to controllerConnection() + coding style fixes

Renamed getControllerConnection() to controllerConnection().
New style & gfx for master vol/pitch sliders, fx front panel artwork
Effect panel & effect window style, new knob images, knobs use palette