Chore: Upgrade powerline configuration

The upgrade to powerline required a complete change in the format of the
powerline configuration.

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Signed-off-by: Jeff Felchner <accounts+git@thekompanee.com>
Bugfix: Issue tracker plugin was missing _sw_vcs_central_repository_url

We'll just call `_sw_git_central_repository_url` for now.

We're also delegating to `_sw_git_central_repository_url` from
`_sw_vcs_central_repository_url`.

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Change-Id:     I68f0795480d749e2713564a512c11185bf4c53c3
Signed-off-by: Jeff Felchner <accounts+git@thekompanee.com>