Various fixes for ngscopeclient startup options

[fredzo]

Hi Andrew,

This PR fixes several Issues around application startup:

• Fix for Make intensity slider value persistent in scopesessions #936
• Fix for Invalid options are ignored #723 (on Windows, it was already fixed on Max/Linux)
• Fix for Option to launch ngscopeclient.exe maximized #749
• Fix for DPI scaling should be configurable or overridable #953

Doc PR is coming along.

What's been done:

• Added serialization of traceAlpha and persistenceDecay to session.
• Fixed console output at startup on Windows (--help / --version + invalid argument reporting).
• Made ngscopeclient start maximized by default at first start (this can be disable by using --no-maximize / -nm command line argument)
• Made ngscopeclient start with last window position and size at next startup (this can be disabled by using --no-restore / -nr)
• To be able to access PreferenceManager from VulkanWindow at startup, PreferenceManager has been made a Singleton
• The restore window size and position logic stores the name and size of the monitor the application was displayed on, to prevent restoring this position if monitor configuration has changed (i.e. prevent opening the window on a monitor that has been disconnected).
• The maximized / fullscreen status of the application is also restored at startup.
• ImGui Automatic DPI scaling is disabled if one of the NGSCOPECLIENT_FONT_SCALE / NGSCOPECLIENT_UI_SCALE environment variable is set, and provided values are applied to font and content scaling.

[fredzo]

As discussed wit @azonenberg on discord, I made the following changes:

• Added a preference setting for window startup mode with 3 options:
  • Widowed (default) ngscopeclient is started in a fixed 1280x720 window,
  • Maximized : ngscopeclient is started maximized on the main screen
  • Last state : ngoscopeclient window is restored in the last position and size.
• Changed command line arguments to:
  • --maximize / -m : force starting in maximized mode
  • --restore / -r : force starting in restored mode