Add build number to current version

[teddyrogers]

Tribler 8.2.3, please could you append the build number to the version string in Settings -> Versions?

There is a reference to, "Old version". What is this, is it redundant, as I have never seen it populated?

[qstokkink]

This screen is mostly useful for porting from older Tribler versions. It looks like this if you have anything to port:

As part of the whole set of "upgrader" features of 8.3.0, we're thinking of removing this tab and moving the information into the status bar on the bottom of the screen.