Absorb/Move CI helper tools into _datalad_buildsupport or alike

[yarikoptic]

there are breadcrumbs of copying/tuning CI setup, like .appveyor across repos derived from this template like http://github.com/datalad/datalad-next/commit/9cd031c5b13268280901967676d717f5d59d068d
so ideally we should centralize location/maintenance of those tools.

I think this template is already too heavy and not feasible easily to be merged continuously into derived from it repos.

thus I think we should absorb tools somewhere. I think we should do that within https://github.com/datalad/datalad-buildsupport which became "more recent" version of now archived https://github.com/datalad/datalad_build_support .

Then we could ship tools/ci etc there and copy/reuse in this repo and then derived ones in a more modular fashion.

WDYT?