(refs #1823) Link submodule to the online repository viewer

Supports following services:
- GitBucket (need to set the base url at the system settings)
- GitHub
- BitBucket
- GitLab.com
If a repository url doesn't match above services, generate a link to the git repository as before.

src/test/scala/gitbucket/core/util/StringUtilSpec.scala

@@ -63,4 +63,24 @@ class StringUtilSpec extends FunSpec {
       assert(StringUtil.extractCloseId("(refs #123)").toSeq == Nil)
     }
   }
+
+  describe("getRepositoryViewerUrl") {
+    val baseUrl = Some("http://localhost:8080")
+    it("should convert GitBucket repository url"){
+      assert(StringUtil.getRepositoryViewerUrl("http://localhost:8080/git/root/gitbucket.git", baseUrl) == "http://localhost:8080/root/gitbucket")
+      assert(StringUtil.getRepositoryViewerUrl("http://root@localhost:8080/git/root/gitbucket.git", baseUrl) == "http://localhost:8080/root/gitbucket")
+    }
+    it("should convert GitHub repository url"){
+      assert(StringUtil.getRepositoryViewerUrl("https://github.com/root/gitbucket.git", baseUrl) == "https://github.com/root/gitbucket")
+      assert(StringUtil.getRepositoryViewerUrl("https://root@github.com/root/gitbucket.git", baseUrl) == "https://github.com/root/gitbucket")
+    }
+    it("should convert BitBucket repository url"){
+      assert(StringUtil.getRepositoryViewerUrl("https://bitbucket.org/root/gitbucket.git", baseUrl) == "https://bitbucket.org/root/gitbucket")
+      assert(StringUtil.getRepositoryViewerUrl("https://root@bitbucket.org/root/gitbucket.git", baseUrl) == "https://bitbucket.org/root/gitbucket")
+    }
+    it("should convert GitLab repository url"){
+      assert(StringUtil.getRepositoryViewerUrl("https://gitlab.com/root/gitbucket.git", baseUrl) == "https://gitlab.com/root/gitbucket")
+      assert(StringUtil.getRepositoryViewerUrl("https://root@gitlab.com/root/gitbucket.git", baseUrl) == "https://gitlab.com/root/gitbucket")
+    }
+  }
 }