Return build coverage in json

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Enhanced build trace

- Automatically refresh trace if status changes, i.e.: from pending to running
- Automatically enable build scroll if status is either pending or running
- Added method to fetch raw build trace
- Handle "\r" in terminal output
- Added scrollable autoscroll button
Fixed line numbering: missing <a></a> (+6 squashed commits)
Squashed commits:
[fb19f2d] Assign onclick to first <p> instead of <div> and use javascript to open folded sections
[1be6758] Better build output
[380652b] Duration
[a35b9ef] Added spinner and open last folded section.
[2125471] Folding
[8d00b43] Line numbering