#641: improve mirrors

[hohwille]

implements #641 and addes the suggested improvements after PR #643 was already merged.
I also found several bugs that I fixed alongside.
For the record: This PR MUST be merged before creating a release as I had to also merge devonfw/ide-mirrors#1 so this PR can build green.

[hohwille]

For some strange reasons I got conflicted with myself (maybe due to odd merges).
Resolving conflicts in the browser is not much fun.
I will double check by compaing my original local FB with this one after merge.

[hohwille]

For some strange reasons I got conflicted with myself (maybe due to odd merges). Resolving conflicts in the browser is not much fun. I will double check by compaing my original local FB with this one after merge.

OK. Verified. Only two new lines have been added due to conflict resolution but otherwise functions file is identical. Other changes are also fine but small and easy to review.

[hohwille]

Build failed with error:

*** Setting up mvn ***

******** ATTENTION ********
ERROR: Download of java in version 11.0.9.1_1 failed after trying 1 mirror(s).

Ouch. There are doEcho statements that should print some messages before this error actually occurrs.
I have to find a way to reproduce this as it did not happen on my machine. May the conflict resolution broke something that I missed.

[hohwille]

I will still address the quiet vs. verbose issue with dependent setups.
FYI: The tests have not been fixed by my last commit (code style) but by this commit devonfw/ide-mirrors@b8059d0

[hohwille]

I have tested this with arbitrary variants and combinations (and found and fixed bugs I made temporary). It is quite astounding how many combinations of tools, versions, operating-systems, etc. we do support.
I will merge this now and would be very happy if some people could then get a latest SNAPSHOT from OSSRH nexus (https://github.com/devonfw/ide/blob/master/documentation/setup.asciidoc#testing-snapshot-releases).