add tray icon

[ReenigneArcher]

Description

This PR adds a system tray icon. There's not much to it right now, but it should open the avenue for tray notifications (e.g. pairing request, stream started, stream ended, etc. etc.).

I used https://github.com/dmikushin/tray which is a cross platform system tray library, but I have not tested this on macOS or Linux yet. I am not sure how to specify the icon image for Linux, or if it's even possible.

Todo:

• Determine why Sunshine doesn't exit cleanly (before merging this)
• Compile on Linux
• Compile on macOS
• Fix runtime error on macOS
• Get icon to appear on macOS (must create tray icon in main thread on macOS dmikushin/tray#10)
  • Unable to get tray icon created on macOS since it requires creating/updating UI elements on the main thread, so forgoing this for now. If anyone has any ideas, feel free to submit a PR.
• Add deps for Flatpak
  • In order to not hold this PR up, Flatpak can be improved later. Some code added to make the tray icon conditional on Linux depending on if the required deps are available.
• Use boost/locale to translate menu entries
  • Can be a later PR.

Screenshot

Windows

Ubuntu

Issues Fixed or Closed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

LizardByte requires that branches be up-to-date before merging. This means that after any PR is merged, this branch
must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated

[ReenigneArcher]

Getting a runtime error on macOS.

2023-03-13 20:58:20.624 sunshine[21904:70290] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'NSWindow drag regions should only be invalidated on the Main Thread!'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007ff80ceb243b __exceptionPreprocess + 242
	1   libobjc.A.dylib                     0x00007ff80ca01e25 objc_exception_throw + 48
	2   CoreFoundation                      0x00007ff80ceda5d6 _CFBundleGetValueForInfoKey + 0
	3   AppKit                              0x00007ff80ff81161 -[NSWindow(NSWindow_Theme) _postWindowNeedsToResetDragMarginsUnlessPostingDisabled] + 307
	4   AppKit                              0x00007ff80ff6df4f -[NSWindow _initContent:styleMask:backing:defer:contentView:] + 1247
	5   AppKit                              0x00007ff80ff6da69 -[NSWindow initWithContentRect:styleMask:backing:defer:] + 42
	6   AppKit                              0x00007ff81071b6fe -[NSStatusBarWindow initForStatusItem:] + 88
	7   AppKit                              0x00007ff81071e623 -[NSStatusItem _initWithStatusBar:length:priority:systemInsertOrder:] + 349
	8   AppKit                              0x00007ff8101daef2 -[NSStatusBar _statusItemWithLength:withPriority:] + 76
	9   sunshine-0.18.4                     0x0000000105a32e1f tray_init + 120
	10  sunshine-0.18.4                     0x00000001059555ce _Z11create_trayv + 29
	11  sunshine-0.18.4                     0x000000010595949f _ZNSt3__1L14__thread_proxyINS_5tupleIJNS_10unique_ptrINS_15__thread_structENS_14default_deleteIS3_EEEEPFivEEEEEEPvSA_ + 36
	12  libsystem_pthread.dylib             0x00007ff80cd5f259 _pthread_start + 125
	13  libsystem_pthread.dylib             0x00007ff80cd5ac7b thread_start + 15
)
libc++abi: terminating with uncaught exception of type NSException
zsh: abort      sunshine

macOS running now... but tray icon is not created and no boost message is printed to stdout...

[ReenigneArcher]

@abusse sorry for the ping, but wondering if you could review this. I'm struggling to get the tray icon created in macOS. macOS doesn't allow creating the icon outside of the main thread, but the tray requires an endless loop for listening to events.

I tried creating the icon in the main thread but running the tray_loop in another thread, but that did not seem to pick up the events for the tray icon.