[bonninr]

Fixes #492.

• Settings windows and the program's other dialogs are above other programs only while Masterpiece is in front. JUCE makes a new dialog always on top whenever another of the program's windows is, and the Recorder and Combinations windows are while the program is in front, so such a dialog stayed above every other program. Each one now follows the program in and out of the front, as those windows do. Windows and macOS; Linux keeps its windows as they are.
• macOS: an open or save panel hides while another program is in front and comes back with Masterpiece. The application installs this once at startup (MacWindows.mm); the plug-in leaves the host's panels alone.

Checked in the program on Windows, GrandOrgue demo, Recorder open, then Organ settings, then another program (Notepad) brought to the front; the topmost flag of each window:

Moment	Organ settings, before	Organ settings, after	Recorder
Masterpiece in front	topmost	topmost	topmost
Notepad in front	topmost: stays above Notepad	not topmost	not topmost
Masterpiece in front again		topmost	topmost

The file dialog part is macOS only: built by the macOS jobs here, and on the Mac test list.

mp_tests --no-perf: 300 run, 0 failed.