feat: add fetchQuickemuVersion() and display version in the menu

[flexiondotorg]

Description

The patch adds fetchQuickemuVersion() and uses it to display the Quickemu version being used by Quickgui.

• Resolves #169

Type of change

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas