Remove loading 3rd party dependency

[ngyikp]

Browsers with stricter privacy settings (such as turning off 3rd party cookies) would block 3rd party connection to https://jimmywarting.github.io/StreamSaver.js/mitm.html?version=2.0.0

Fix this issue by self-hosting these files:

• https://github.com/jimmywarting/StreamSaver.js/blob/eea84e9ba76819cae0cab39e9e827d7b5e3d588b/mitm.html
• https://github.com/jimmywarting/StreamSaver.js/blob/eea84e9ba76819cae0cab39e9e827d7b5e3d588b/sw.js