Specify path for project homepage buttons

I think, a good feature can be to allow the user to select the content or path for some of the buttons on project page.

That's something similar to gitlab-ce#24414 but it not the same feature.

My question are to allow, for example, when you go to project page, to see README, CHANGELOG, LICENSE buttons (and others, I think), but allowing these files to not be on the root of the repository.

For example, some users can have a LICENSE.txt file, or have CHANGELOG file on another path (on a documentation folder is an option). With the actual system, the repository doesn't show the buttons for these files if the files are not in the root of the repo or if the files doesn't have a standard name.

I think, the actual behavior with README file are not bad. If on the folder you're viewing there's a README file, it's showed below the files. But a good option can be for the root of repository, if there's not a README file on these path, show the configured one on the button itself.

With this feature, users can have a more organized repository without loss of functionality of gitlab.