Release 2.3

This MR contains all remaining items for the Steca Release 2.2.5. I laid it out in this issue

After this there would be only one left thing to do: change the date of the Release for 2.2.5 in CHANGELOG.txt and in the Online Documentation. This would be the last thing to do after you have approved of this.

I've tested it on Linux (and Windows today too) for some days without producing any crashes

Resolve #77 (closed) #67 (closed) #71 (closed) #64 (closed) #79 (closed) #84 (closed) #78 (closed) #76 (closed) #93 (closed)

Edit 5th of June 2023: Due to Joachim's request: Change new Version number from 2.2.5 to 2.3 and adapt the title of this MR from "Release 2.2.5" to "Release 2.3"