[Linux] Add seperators to tray, add tray option to reopen app and settings, prevent duplicate instances of app from being opened

[jazzysoggy]

This pull request would add additional functionality and quality of life enhancements to the Linux application:

• Allows for an existing app instance to be reopened from the app tray to the main app menu or settings menu
• Add separators between different options in tray to improve clarity
• Add detection for existing app instances and the ability for a duplicate instance to trigger a reopening of the original app instance instead of spinning up a new instance

This improves functionality for an end user by adding in expected responses to app interactions.

Edit:
Additional changes made since original pull request:

• Add error handling for socket and server
• Use environment variable instead of preprocessor to detect
• Clear variable on original instance quitting
• Proper handling in case connection refused for duplicate client

[tim-gromeyer]

But thank you for your contribution

[kavishdevar]

thanks for the pr! @tim-gromeyer merge it whenever you'd like