Only import playlists from configured paths in option PlaylistsPath. Closes #1181

Syntax is Ant-style Globs, with support for '**' (any subfolder). Default: '.:**' (or '.;**' in Windows`, meaning all folders and subfolders under `MusicFolder`

tests/fixtures/playlists/subfolder1/pls1.m3u

@@ -0,0 +1,2 @@
+test.mp3
+test.ogg

tests/fixtures/playlists/subfolder2/pls2.m3u

@@ -0,0 +1,2 @@
+test.mp3
+test.ogg

tests/mock_persistence.go

@@ -14,6 +14,7 @@ type MockDataStore struct {
 	MockedUser           model.UserRepository
 	MockedProperty       model.PropertyRepository
 	MockedPlayer         model.PlayerRepository
+	MockedPlaylist       model.PlaylistRepository
 	MockedShare          model.ShareRepository
 	MockedTranscoding    model.TranscodingRepository
 	MockedUserProps      model.UserPropsRepository
@@ -53,7 +54,10 @@ func (db *MockDataStore) Genre(context.Context) model.GenreRepository {
 }
 
 func (db *MockDataStore) Playlist(context.Context) model.PlaylistRepository {
-	return struct{ model.PlaylistRepository }{}
+	if db.MockedPlaylist == nil {
+		db.MockedPlaylist = struct{ model.PlaylistRepository }{}
+	}
+	return db.MockedPlaylist
 }
 
 func (db *MockDataStore) PlayQueue(context.Context) model.PlayQueueRepository {