Prevent multiple instances of app

[vertopolkaLF]

Describe the bug

Right now there could be infinite amount of app running at the same time. This doesn't make any sense to run more than one

Steps to reproduce

1. Launch the app
2. Launch the app again
3. 2 instances of the same app running

Expected behavior

App already running, no need to run it again

Screenshots

Operating system

Windows

Version of Qopy

0.3.3

Additional context

No response