Partially addresses #47424.

Closes gitaly#958

The special characters of a wiki title are now escaped correctly.

- Added method to check if the current Page version is the current latest version
- Conditionally checks for current version when showing Edit button
- Added feature specs for viewing project wiki page and expect edit button
- Added Changelog

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

* Add WikiPage#id method returning associated SHA for wiki page commit

1. So we can build the markdown preview URL for it.

2. We can't skip the slug in this case, because the slug is used to
construct relative markdown URLs.

3. Add rspec feature tests to cover creating wiki pages with
   spaces/hyphens in the name.

4. Add rspec feature tests for markdown preview URL rewriting, which was
   only covered by unit tests up to this point.

update changelog