Adds Lyrics Support to Subsonic API (#1379)

* Add function 'isSynced' that identifies if lyrics are synced or not and add tests for the same

* implement 'getLyrics' which returns lyrics if they exist

Signed-off-by: Dheeraj Lalwani <lalwanidheeraj1234@gmail.com>

* remove timestamps frorom the the lyrics if they are synced, fix filters & clean up code

Signed-off-by: Dheeraj Lalwani <lalwanidheeraj1234@gmail.com>

* add snapshot tests for the 'Lyrics' response & add some clean up

Signed-off-by: Dheeraj Lalwani <lalwanidheeraj1234@gmail.com>

* add tests for 'GetLyrics' function

Signed-off-by: Dheeraj Lalwani <lalwanidheeraj1234@gmail.com>

* update the snapshot test & the test for 'GetLyrics' function

Signed-off-by: Dheeraj Lalwani <lalwanidheeraj1234@gmail.com>

server/subsonic/responses/responses.go

@@ -46,6 +46,7 @@ type Subsonic struct {
 	PlayQueue  *PlayQueue  `xml:"playQueue,omitempty"                                     json:"playQueue,omitempty"`
 	Bookmarks  *Bookmarks  `xml:"bookmarks,omitempty"                                     json:"bookmarks,omitempty"`
 	ScanStatus *ScanStatus `xml:"scanStatus,omitempty"                                    json:"scanStatus,omitempty"`
+	Lyrics     *Lyrics     `xml:"lyrics,omitempty"                                        json:"lyrics,omitempty"`
 }
 
 type JsonWrapper struct {
@@ -346,3 +347,9 @@ type ScanStatus struct {
 	FolderCount int64      `xml:"folderCount,attr"         json:"folderCount"`
 	LastScan    *time.Time `xml:"lastScan,attr,omitempty"  json:"lastScan,omitempty"`
 }
+
+type Lyrics struct {
+	Artist string `xml:"artist,omitempty,attr"  json:"artist,omitempty"`
+	Title  string `xml:"title,omitempty,attr"   json:"title,omitempty"`
+	Value  string `xml:",chardata"              json:"value"`
+}