* add Range= to log, making responses a lot smaller for massive rooms
* switch xhr to fetch
* post the form using fetch if possible
* also refresh log faster while waiting for command echo / response
* do not follow redirect, saving a request
* do not post empty body
* smooth-scroll the log view
* paste the log into the div when loading the HTML (up to 1MB, rest will be `fetch`ed)
* fix duplicate charset in display_log response
