convert functon creation to python

The new functions always creates normal and partitioned functions.
Also adds specialised connection and cursor classes for adding
frequently used helper functions.

test/python/test_db_connection.py

@@ -0,0 +1,32 @@
+"""
+Tests for specialised conenction and cursor classes.
+"""
+import pytest
+
+from nominatim.db.connection import connect
+
+@pytest.fixture
+def db(temp_db):
+    conn = connect('dbname=' + temp_db)
+    yield conn
+    conn.close()
+
+
+def test_connection_table_exists(db, temp_db_cursor):
+    assert db.table_exists('foobar') == False
+
+    temp_db_cursor.execute('CREATE TABLE foobar (id INT)')
+
+    assert db.table_exists('foobar') == True
+
+
+def test_cursor_scalar(db, temp_db_cursor):
+    temp_db_cursor.execute('CREATE TABLE dummy (id INT)')
+
+    with db.cursor() as cur:
+        assert cur.scalar('SELECT count(*) FROM dummy') == 0
+
+def test_cursor_scalar_many_rows(db):
+    with db.cursor() as cur:
+        with pytest.raises(ValueError):
+            cur.scalar('SELECT * FROM pg_tables')