Implement git refs API for listing references (branches, tags and other) (#5354)

* Inital routes to git refs api

* Git refs API implementation

* Update swagger

* Fix copyright

* Make swagger happy add basic test

* Fix test

* Fix test again :)

vendor/gopkg.in/src-d/go-git.v4/plumbing/storer/index.go

@@ -0,0 +1,9 @@
+package storer
+
+import "gopkg.in/src-d/go-git.v4/plumbing/format/index"
+
+// IndexStorer generic storage of index.Index
+type IndexStorer interface {
+	SetIndex(*index.Index) error
+	Index() (*index.Index, error)
+}