Create terminal.py to run bots in the terminal.

This program replaces zulip_bot_output.py, which had
gotten a little out of date.

It should be able to simulate a terminal conversation for
all of our bots, including those that use "advanced" features:

    third party config files: tested with giphy
    message updates: tested with incrementor
    storage: tested with virtual_fs and others

zulip_bots/setup.py

@@ -36,7 +36,7 @@ package_info = dict(
     entry_points={
         'console_scripts': [
             'zulip-run-bot=zulip_bots.run:main',
-            'zulip-bot-output=zulip_bots.zulip_bot_output:main'
+            'zulip-terminal=zulip_bots.terminal:main'
         ],
     },
     include_package_data=True,