[dzil] add github_user overrides; use GitHubMeta plugin

Anything using this bundle is liable to be a package I own -- including
packages others may upload to the CPAN.  In the case that it's not, we setting
set_github_user to false will defer to the plugin's judgment, while setting
github_user to a different userid will cause that id to be used instead of
mine (e.g. for an organization or the like).
move our dependency listing from the bundle to the dist.ini

... well, most of them, at any rate.
Move Pod::Weaver deps into dist.ini
Add a helper role for Git::Raw operations