Merge pull request #500 from diizy/stable-0.4

Piano widget: fix velocity, Opulenz: increase volume
Revert "Do not display ENV/LFO tab in plugin window if controls are disabled in it (SF2 Player and OpulenZ)"

This does not work well if you open an instrument window of a single
streamed instrument, close it afterwards and open an instrument window
of a regular instrument due to widget caching/reuse. We therefore have
to find a better solution which allows dynamically showing/hiding tabs
in the TabWidget class. Until then restore the previous behaviour.

This reverts commit ed29f2b6f6aa8e93817dfc1c14ccf49de40b800f.
InstrumentSoundShapingView: display info about single-streamed instruments

Until we have a solution for hiding the ENV/LFO tab, display a sensible
message at least.
Made 1.0.0 release

After almost exactly 10 years of development, we proudly bump the version
number to 1.0.0.