Basic playlist deduplication

Before adding songs to the playlist, check if the playlist already
contains the song id.

libsaria/collection/collection.py

@@ -101,6 +101,9 @@ class Collection:
 			return None
 		return res[0]
 
+	def has_id(self, id):
+		return id in self.index
+
 	def get_attr(self, id, attr):
 		rec = self.records[id]
 		if attr == "filepath":
@@ -124,6 +127,8 @@ class Collection:
 			return tags[2]
 
 	def insert_tags(self, artist, album, title, id):
+		if self.has_id(id) == True:
+			return
 		tags = self.tag_tree.insert([artist, album, title, id])
 		self.index.insert([artist, album, title], id)
 		self.size += 1