Item7855: Refactoring the PSGI contrib, Windows standalone distribution, and TWiki dev stuff

The effort to create an easy-to-install and easy-to-create standalone TWiki for Windows has resulted in three extensions:

1. The PSGIEngineContrib allows to run TWiki with a Perl webserver, therefore avoiding the configuration hassle for Apache et al.
2. TWPDistrib contains the driver script for the webserver, a MANIFEST listing all TWiki components included in the distribution, and an initial LocalSite.cfg.orig.
3. Two subcommands in TWikiDevContrib, collect and packtwp, allow easy creation of the Windows executable.

All that being work in progress at the same time, the borders between the extensions got somewhat blurred.

• The PSGI Engine Contrib contains a module TWiki::Contrib::PSGIEngineContrib::PARLoader which is not needed to run TWiki as a PSGI application. It is only required to build the executable with CPAN:Par::Packer and should therefore be removed from the Engine. The code of PARLoader depends on the Perl version and, to some extent, the versions of CPAN modules used by the distribution, but not on the TWiki version.
• The TWikiDevContrib does not depend on any TWiki code nor version and can therefore be built and installed with standard Perl mechanisms; right now it is prepared for CPAN:Dist::Zilla. It must be installed on Windows to create the Windows executable. Recent additions to the same Contrib have nothing to do with creating the executable, but they bring a load of new dependencies. It should be considered to separate the different sections (patch management, building, managing test VMs) into different extensions. Like many contribs, this one is independent of TWiki versions, but unlike all others it is also independent of TWiki modules.

-- TWiki:Main/HaraldJoerg - 2018-08-31