BC Breaks should be shown on self-update

[alexander-schranz]

when you do a self-update and have a bc break it should be shown the https://github.com/nanbando/core/blob/master/UPGRADE.md text.

[wachterjohannes]

we could add the BC-Breaks as a md-file to the release and display it. that would not work if you update to nightly version.