Link to issues and wikis with project ids instead of names
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### Problem to solve
I want to be able to link into project's other pages than just the home page. /projects/4/issues currently does not work, but it should. I have an external application that integrates with gitlab that we use to help with development, but there isn't a way to link to issues or wiki pages without using the brittle name based links.
### Intended users
Everyone who needs to be linked from an external application directly into gitlab.
### Further details
This can be worked around by saving the project namespace externally and then making a system webhook to update the name whenever it's changed, but it seems so much simpler to just have the projects/id user work. It's pretty inconsistent that the projects/id work but inner links do not.
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