Fix layout
[Fix #487] Do not recenter after error list navigation

Preserve the position if the user is inside the error list
Properly pass package names to errcheck

Work around https://github.com/kisielk/errcheck/issues/45
Fix comment

[ci skip]
Fix indentation
Improve docstring

[ci skip]
[Fix #492] Do not needlessly recenter the error list

Only recenter if there are really some errors to move into the visible
part of the window.
Force-install all APT packages

It's a throw-away testing VM, so this won't do no harm, and avoids
hassles with broken upstream repos.  CFEngine, looking at you here!

See #496
Force-update the cache
Fix contribution requirements for provisioning

Thanks, @Wilfred

[ci skip]
[Fix #497] Handle empty messages from Clang
Fix style

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First try att dscanner
Use both --syntaxCheck and --styleCheck instead of -s
Remove --styleCheck. Both arguments are not supported.
Add d-dscanner-syntax and d-dscanner-style
Add d-dscanner-style to flycheck-checkers
Defined :next-checkers to d-dmd
Add URL ref for DScanner checkers
Correct use of :next-checkers for D checkers