Datalad-mihextras

- The fetch/push-anywhere functionality (`XDLRA` git-annex backend and `datalad-annex::` Git remote helper) has been remove. It has been reworked and improved, and is now released as part of https://github.com/datalad/datalad-next (version 0.2.0)
- The `export-to-webdav` has been discontinued, and is no longer shipped with this extension. A superior and more standard approach is available from https://github.com/datalad/datalad-next (version 0.2.0), which provides a `create-sibling-webdav` command, and enhanced the standard `push` command to be able to automatically export to special remotes.

- New Git remote helper `git-remote-datalad-annex` that enables using any git-annex special remote as a regular Git remote.
- New git-annex `XDLRA` backend, exclusively for use with `git-remote-datalad-annex`.
- Add basic test for snakemake wrapper.
- Improve cross-platform robustness of test.

- New `x-export-bagit` command draft
- Make tests degrade gracefully, when no WEBDAV credentials are available

No longer use `tests_require` but a `devel` flavor of `extras_require`.

New dataset procedure configures a dataset for use as a KDENLIVE project. Most importantly it configures the dataset clone to not commit the absolute root path configured in a project file into Git. Instead, a placeholder is stored that is replaced with the absolute path of the dataset root location on checkout. This makes KDENLIVE project datasets portable.

A new command to export a dataset to a WEBDAV enabled HTTP server.