Small updates to modernise the codebase.

This update primarily modernises the codebase under the hood. There are also some minor improvements to the interface.

Quaver now supports many less common scales. Improvements to the internal synthesiser. The minimum version of macOS is now 10.13.

Many minor updates and improvements.

Support for Dark Mode on macOS 10.14 Mojave

Quaver can now convert time durations between milliseconds and samples at a variety of sample rates. Other minor improvements.

You can now use a MIDI device to tap tempo

Fixes a bug where the on-screen keyboard in the Pitch tab would sometimes not initialise correctly.

Quaver now includes a synthesiser. This allows you to hear notes as you make your selection in the pitch view. You can also preview scales in the scale view. Quaver also now accepts input fro MIDI devices. You can use a MIDI keyboard to make selections in the pitch view.

Fixes a bug in the handling of negative octaves in the pitch view.

Quaver now has a metronome in the tempo tab.

You can now choose which definition of middle C you want the Pitch tool to use. Middle C can be defined as C3, C4 or C5.