Added front-end test "Draw a path"

Closing #34 as it looks good. We need a lot more tests though which can be their own issues.

This also includes a fix for paths that are drawn quicker than 100ms are not being sent to the server and other clients (yay!). It was a showstopper for the test because the script to drag the mouse did it in like nanoseconds.

Add it to the server and then use it the same way that you would Etherpad Lite:

```
http://localhost:3000/tests/frontend
```
or
```
http://draw.etherpad.org/tests/frontend
```