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.
Browser detection by operating system

Close #38.