Console report enhancements

Added:
- print remaining tests countdown (per-browser and total)
- print browser name and version
- print test elapsed time
- mark long-running tests (over configurable threshold) with a different color
- logging of connected and better logging of disconnected slaves
- log unfinished tests instead of undispatched
- print campaign elapsed time at the end

We used to log the number of tests that have not started yet instead of
ones that were finished, which led to incorrect numbers especially when
using multiple browsers at the same time.

Now this is corrected both in the console and Attester status page.

Close #13. Close #29.
Better logging on the slave

Redesign the slave interface to have a clear understanding on what's happening on the slave.
This is obtained enabling console.log and writing logs in a div when the URL parameter `log` is set to `true`.

If also adds additional elements in the page that can be used to query the status of the slave with tools like selenium.
An invisilbe element with id `status_info` contains another element with id

`_info_[status]`

Possible values for `status` are:
* `loading` when the slave is trying to connect
* `connected` or `disconnected` as soon as socket.io establishes or looses a connection
* `executing` while running a test
* `idle` after a test has been executed

Close #41
Fix typo and undefined value