Server sometimes returns 304, which causes a blank screen on the Island web UI

[ShayNehmad]

Describe the bug

See the following logs:

2020-02-24 10:19:07,131 - environment.py:46 -   <module>() - INFO - Monkey's env is: StandardEnvironment
2020-02-24 10:19:09,188 - main.py:85 - assert_mongo_db_version() - INFO - Mongo DB version OK. Got ...
2020-02-24 10:19:09,338 - main.py:60 - log_init_info() - INFO - Monkey Island Server is running. Listening on the following URLs: 
2020-02-24 10:19:35,213 - wsgi.py:374 -       _log() - INFO - 304 GET / (::1) 216.00ms
2020-02-24 10:21:43,865 - wsgi.py:374 -       _log() - INFO - 304 GET / (::1) 3.00ms
2020-02-24 10:21:43,878 - wsgi.py:374 -       _log() - INFO - 304 GET /main.js (::1) 2.00ms
2020-02-24 10:21:44,976 - wsgi.py:374 -       _log() - INFO - 304 GET /8d3a215954e538c692197fc6fba38732.svg (::1) 5.00ms
2020-02-24 10:21:45,026 - wsgi.py:374 -       _log() - INFO - 304 GET /186d5841bfbd494cdbb8e5284f50d30b.svg (::1) 3.00ms
2020-02-24 10:21:45,213 - wsgi.py:374 -       _log() - INFO - 304 GET /b30dd0811bb67a69d1549c86bcc2fd2b.png (::1) 3.00ms
2020-02-24 10:21:51,322 - wsgi.py:374 -       _log() - INFO - 304 GET / (::1) 2.00ms
2020-02-24 10:21:51,368 - wsgi.py:374 -       _log() - INFO - 304 GET /main.js (::1) 3.00ms
2020-02-24 10:21:52,184 - wsgi.py:374 -       _log() - INFO - 304 GET /8d3a215954e538c692197fc6fba38732.svg (::1) 3.00ms
2020-02-24 10:21:52,194 - wsgi.py:374 -       _log() - INFO - 304 GET /186d5841bfbd494cdbb8e5284f50d30b.svg (::1) 3.00ms
2020-02-24 10:21:52,332 - wsgi.py:374 -       _log() - INFO - 304 GET /b30dd0811bb67a69d1549c86bcc2fd2b.png (::1) 3.00ms

To Reproduce

Steps to reproduce the behavior:

1. Install Monkey 1.7.0 using Windows installer
2. Access Island using XXX browser
3. Blank screen

Expected behavior

No 304 should be sent practically always. Caching is probably bad for us since the information changes dynamically and drastically.

Screenshots

Machine version (please complete the following information):

• OS: Windows