Gitlab code viewer should enable devs to click through to other classes within the same repository
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### Proposal
When devs are looking at a codebase through GitLab's UI they often want to follow classes by click on them as you can do in GitHub.
1. Open https://github.com/gitlab4j/gitlab4j-api/blob/master/src/main/java/org/gitlab4j/api/AbstractApi.java
1. Click on "UrlEncoder"
1. See the Definition and References
1. Be able to click to the definition or references
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