[Feature] Add version information to Help menu

[banjaxedben]

Motivation

When raising an issue or checking for open issues in GitHub, it is necessary to know the version of the application I am using.
I can't see the version information anywhere!

Detailed design

The Help menu should have an "About MQTTX" item, which when selected will display the version number.
e.g. v1.9.10

[ysfscream]

You can find it in the "About" menu at the bottom, thanks for using.