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/storage/filesystem/reference.go

@@ -0,0 +1,44 @@
+package filesystem
+
+import (
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+	"gopkg.in/src-d/go-git.v4/storage/filesystem/dotgit"
+)
+
+type ReferenceStorage struct {
+	dir *dotgit.DotGit
+}
+
+func (r *ReferenceStorage) SetReference(ref *plumbing.Reference) error {
+	return r.dir.SetRef(ref, nil)
+}
+
+func (r *ReferenceStorage) CheckAndSetReference(ref, old *plumbing.Reference) error {
+	return r.dir.SetRef(ref, old)
+}
+
+func (r *ReferenceStorage) Reference(n plumbing.ReferenceName) (*plumbing.Reference, error) {
+	return r.dir.Ref(n)
+}
+
+func (r *ReferenceStorage) IterReferences() (storer.ReferenceIter, error) {
+	refs, err := r.dir.Refs()
+	if err != nil {
+		return nil, err
+	}
+
+	return storer.NewReferenceSliceIter(refs), nil
+}
+
+func (r *ReferenceStorage) RemoveReference(n plumbing.ReferenceName) error {
+	return r.dir.RemoveRef(n)
+}
+
+func (r *ReferenceStorage) CountLooseRefs() (int, error) {
+	return r.dir.CountLooseRefs()
+}
+
+func (r *ReferenceStorage) PackRefs() error {
+	return r.dir.PackRefs()
+}