Make InstrumentTrackWindow as large as the InstrumentView requires

Previously, they had been resized by the fixed size parent tab widget. We need
to do this manually now.

- Fix the instrument window tabs minimum width and height formulae
- Also set minimum height and width for instrument tab

In the instrument plugin tab, there was an orange stripe for
TripleOscillator. This was because internally, TabWidget moves up the
widget by 1 (TabWidget.cpp, line 89).

The size of the whole window is:

```
widget->height() + m_tabbarHeight - 1
```

So this code adds an offset of "-1" to the necessary computations.