playlist: Create a FilterEntry entry

This derives from the lib.filter.Entry to set the playlist filter and
increase the margins.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

playlist/header.py

@@ -0,0 +1,10 @@
+# Copyright 2021 (c) Anna Schumaker.
+import lib
+from . import model
+
+class FilterEntry(lib.filter.Entry):
+    def __init__(self):
+        lib.filter.Entry.__init__(self, model.PlaylistFilter)
+        self.set_margin_start(200)
+        self.set_margin_end(200)
+        self.set_hexpand(True)

playlist/test_header.py

@@ -0,0 +1,14 @@
+# Copyright 2021 (c) Anna Schumaker.
+import lib
+import unittest
+from . import header
+from . import model
+
+class TestFilterEntry(unittest.TestCase):
+    def test_init(self):
+        entry = header.FilterEntry()
+        self.assertIsInstance(entry, lib.filter.Entry)
+        self.assertEqual(entry.filter, model.PlaylistFilter)
+        self.assertEqual(entry.get_margin_start(), 200)
+        self.assertEqual(entry.get_margin_end(), 200)
+        self.assertTrue(entry.get_hexpand())