Initial API-centric/JSON overhaul, 2FA login.

With #83, we need a new approach to allow this program to function.
This is the first attempt. Some features have been broken or removed,
and likely cannot be added back. Cards, embedded tweets, etc. have been
dropped, and it's possible that stickers are broken too (do they even
exist anymore?).

I can't promise that this works robustly, but it was tested in Python
3.7 with a saved session; I'm also not sure authentication isn't
totally broken as I tried to implement a 2FA fix, too, but locked
my account out from too many login attempts before I managed to get it
working.

dmarchiver/cmdline.py

@@ -12,15 +12,14 @@
                             Conversation ID
       -u,  --username       Username (e-mail or handle)
       -p,  --password       Password
+      -t,  --token          2FA token code (optional)
       -d,  --delay          Delay between requests (seconds)
       -s,  --save-session   Save the session locally
       -di, --download-images
                             Download images
       -dg, --download-gifs  Download GIFs (as MP4)
       -dv, --download-videos
                             Download videos (as MP4)
-	  -th,  --twitter-handle     
-	                        Use the Twitter handles instead of the display names	
       -r, --raw-output  Write the raw HTML to a file
 """
 
@@ -44,6 +43,7 @@ def main():
     parser.add_argument("-id", "--conversation_id", help="Conversation ID")
     parser.add_argument("-u", "--username", help="Username (e-mail or handle)")
     parser.add_argument("-p", "--password", help="Password")
+    parser.add_argument("-t", "--token", default=None, help="2FA token")
     parser.add_argument("-d", "--delay", type=float, default=0, help="Delay between requests (seconds)")
     parser.add_argument(
         "-s",
@@ -94,7 +94,7 @@ def main():
 
     crawler = Crawler()
     try:
-        crawler.authenticate(username, password, args.save_session, args.raw_output)
+        crawler.authenticate(username, password, args.save_session, args.raw_output, args.token)
     except PermissionError as err:
         print('Error: {0}'.format(err.args[0]))
         print('Exiting.')
@@ -113,15 +113,15 @@ def main():
                 conversation_id,
                 args.delay,
                 args.download_images,
-                args.download_gifs, args.download_videos, args.twitter_handle, args.raw_output)
+                args.download_gifs, args.download_videos, args.raw_output)
         else:
             print('Conversation ID not specified. Retrieving all the threads.')
             threads = crawler.get_threads(args.delay, args.raw_output)
             print('{0} thread(s) found.'.format(len(threads)))
 
             for thread_id in threads:
                 crawler.crawl(thread_id, args.delay, args.download_images,
-                              args.download_gifs, args.download_videos, args.twitter_handle, args.raw_output)
+                              args.download_gifs, args.download_videos, args.raw_output)
                 time.sleep(args.delay)
     except KeyboardInterrupt:
         print('Script execution interruption requested. Exiting.')