Feature/provider selection

[croesnick]

PR Checklist

Please check if your PR fulfills the following requirements:

• [X] Tests for the changes have been added (for bug fixes / features)
• [X] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• [ ] Bugfix
• [X] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Other... Please describe:

What is the current behavior?

Currently, only git repositories are supported.

What is the new behavior?

But in my uses cases, I additionally need svn and also git-svn (as a proxy for svn repos). This PR adds both. It moreover disables all git-related functions (gitlab export and alike) when the provider is not git.

Does this PR introduce a breaking change?

• [X] Yes
• [ ] No

• Column sha in CSV has been renamed to revision. I though about deprecating the sha column, but then then new revision column would needed to go to the end of the csv, which IMHO is not ideal. Rationale for just doing the renaming has been that the upgrade path after this change is very easy: simply rename sha to revision in the csv and we are good to go. In case this is still an inconvenience, we could handle the revision being stored either in the revision or sha property when loading the csv and just not telling the user about it.
• Configuration option code-review.gitDirectory has been moved to code-review.vcs.git.directory

Other information

[d-koppenhagen]

@croesnick I recently merged some other features/fixes, so a rebase is needed. To not beak the DevEx for current consumers, the adoption from the sha to revision CSV Header name should be done automatically, when reading existing comments.