Add possibility to resume recording

[jstaerk]

When clicking record I somehow always received a "The AudioContext was not allowed to start. It must be resumed (or created) after a user gesture on the page. https://goo.gl/7K7WLu" on the dev console, even after I restarted my PC. On my Win 10 64 bit Chrome 74.0.3729.157 that resulted in 0 Seconds, 44 bytes wav files. After adding the proposed resume button and clicking record after clicking resume it seems to work.