Update internal links when cloning regions

[timobrembeck]

Short description

This adds a few utils for link replacements and applies the replacement mechanism on cloned regions.

Proposed changes

• Add utility function to replace links in content
• Update internal links when cloning regions
• Add management command to replace links in content

Side effects

Well, testing this was quite a journey. The main problem was that our normal test cases not not allow interactions with the database, and I noticed very weird side effects from enabling transaction support only for few test cases.
In particular, the problem was that the transaction test cases roll back not only the changes from the particular test case, but also remove the test data including the roles that are generated during the migrations.
I think I now got around them by adding the extension pytest-order and telling pytest it should execute the transaction test cases last. Also, I needed to provide another test fixture just for roles to make sure I can re-populate the database after it has been rolled back by another transaction test case.

Resolved issues

Fixes: #1383

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Code Climate has analyzed commit 92ec85c and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 76.1% (0.2% change).

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[JoeyStk]

Thank you a lot! This is a very important feature!
To be honest this is a little bit above my head. I still tried my best and for me everything seemed to work, but it would be good if someone else could have a closer look

[MizukiTemma]

Thank you for PR 😃 This is a very nice feature!
Link replace works as expected during region cloning and by command.

I just noticed one case (this is not your fault, though).
When the source regions has no impressum, replace_links will not be run. In this case an attribute error will be shown but a new region will be created with not updated links. I think this happens with source reagions without page (or language_tree) too.

How to reproduce:

1. Go to the region Nürnberg (default data, no impressum).
2. Put some internal links in a page.
3. Clone Nürnberg, entounter to an attribute error.
4. Return and see unupdated links in the page in the new region.

Please dismiss this if an error page is enough or we can assume that a source region has always language_tree, page and impressum.

[timobrembeck]

@MizukiTemma Thanks a lot for the report, since this is a separate problem that already exists on the develop branch, I opened issue #2153 for this and fixed it in #2154.