feat: use cobra to provide subcommands, move sources to lib (#506)

- Use cobra in order to provide subcommands `serve` and `db`.
  - Subdir `cmd` is removed.
  - Subdir `cli` is created, which is a standard cobra structure.
- Sources related to the core are moved to subdir `lib`.
- #497 and #504 are merged.
- Deprecated flags are added. See https://github.com/filebrowser/filebrowser/pull/497#discussion_r209428120.
- [`viper.BindPFlags`](https://godoc.org/github.com/spf13/viper#BindPFlags) is used in order to reduce the verbosity in `serve.go`.

lib/bolt/share.go

@@ -0,0 +1,66 @@
+package bolt
+
+import (
+	"github.com/asdine/storm"
+	"github.com/asdine/storm/q"
+	fb "github.com/filebrowser/filebrowser/lib"
+)
+
+// ShareStore is a shareable links store.
+type ShareStore struct {
+	DB *storm.DB
+}
+
+// Get gets a Share Link from an hash.
+func (s ShareStore) Get(hash string) (*fb.ShareLink, error) {
+	var v fb.ShareLink
+	err := s.DB.One("Hash", hash, &v)
+	if err == storm.ErrNotFound {
+		return nil, fb.ErrNotExist
+	}
+
+	return &v, err
+}
+
+// GetPermanent gets the permanent link from a path.
+func (s ShareStore) GetPermanent(path string) (*fb.ShareLink, error) {
+	var v fb.ShareLink
+	err := s.DB.Select(q.Eq("Path", path), q.Eq("Expires", false)).First(&v)
+	if err == storm.ErrNotFound {
+		return nil, fb.ErrNotExist
+	}
+
+	return &v, err
+}
+
+// GetByPath gets all the links for a specific path.
+func (s ShareStore) GetByPath(hash string) ([]*fb.ShareLink, error) {
+	var v []*fb.ShareLink
+	err := s.DB.Find("Path", hash, &v)
+	if err == storm.ErrNotFound {
+		return v, fb.ErrNotExist
+	}
+
+	return v, err
+}
+
+// Gets retrieves all the shareable links.
+func (s ShareStore) Gets() ([]*fb.ShareLink, error) {
+	var v []*fb.ShareLink
+	err := s.DB.All(&v)
+	if err == storm.ErrNotFound {
+		return v, fb.ErrNotExist
+	}
+
+	return v, err
+}
+
+// Save stores a Share Link on the database.
+func (s ShareStore) Save(l *fb.ShareLink) error {
+	return s.DB.Save(l)
+}
+
+// Delete deletes a Share Link from the database.
+func (s ShareStore) Delete(hash string) error {
+	return s.DB.DeleteStruct(&fb.ShareLink{Hash: hash})
+}