Make streaming optional for the /chat endpoint (#287)

* Update the /chat endpoint to conditionally support streaming

- If streams are enabled, return the threadgenerator as it does currently
- If stream is disabled, return a JSON response with the response/compiled references separated out
- Correspondingly, update the chat.html UI to use the streamed API, as well as Obsidian
- Rename chat/init/ to chat/history

* Update khoj.el to use the /history endpoint

- Update corresponding unit tests to use stream=true

* Remove & from call to /chat for obsidian

* Abstract functions out into a helpers.py file and clean up some of the error-catching

tests/test_chat_actors.py

@@ -174,6 +174,8 @@ def test_generate_search_query_with_date_and_context_from_chat_history():
     expected_responses = [
         ("dt>='2000-04-01'", "dt<'2000-05-01'"),
         ("dt>='2000-04-01'", "dt<='2000-04-30'"),
+        ('dt>="2000-04-01"', 'dt<"2000-05-01"'),
+        ('dt>="2000-04-01"', 'dt<="2000-04-30"'),
     ]
     assert len(response) == 1
     assert "Masai Mara" in response[0]