Moving empty destructors out of the .cpp files and into headers
allows them to be devirtualized in certain cases.
(When the compiler can't "see" a function in a header, it must largely
assume it's some black box that the linker will resolve.)
While we're at it, use C++11's `= default` to define empty virtual
desturctors for us.
For some classes (e.g., Piano), nothing is derived from it, so we can
mark the class as final and remove any explicit virtual dtor.
There are many other places where this can be done, but this is a large
enough patch as-is.
Adjust PatternView::update to show the name of the pattern as the tool
tip (regardless of whether it is a beat and bassline or a melody
pattern).
Override the public slot TrackContentObjectView::update for
AutomationPatternView and BBTCOView. Implement it similar to
PatternView::update.
Lukas W