Updates based on a full run of the browser tests

I've re-run the browser tests, after a 2 hour wait ... the full results are here:

https://gist.github.com/ColinEberhardt/133147b629560b6def9d

Quick summary:

```
passed: 1135/1624
failed: 489/1624
new issues: 349
resolved issues: 19
```

Regarding the resolved issues, I have updated `knownIssues.js` to reflect this. I have also closed #819 and #824 as a result.

Regarding the 349 new issues (!!!!!) I need to do a bit of investigation. It is most likely that the tests need to be tweaked a little.

I have also modified the logic for clearing a todo item to use delete and backspace. This is required because the spec does not dictate the initial cursor position when a todo item enters into edit mode.