Allow expanding/hiding groups in the timing tab about buildbuddy

[siggisim]

Hey Josh - I partially addressed this in (hasn't made it to the Docker image yet):
90436e5

I'll need to mess around with the page sizes a bit to see what makes sense (might add a toggle there as well).

Great suggestion on the group merging, will leave this open until all points have been addressed.

[siggisim]

Hey @Qinusty

Added grouping options and page size controls in commit 5b5a237

This allows you to select whether you want to group by thread or merge all groups. It also allows you to select how many events you want to see per thread.

That should address all of the concerns raised in this issue - let me know if you have others!

Here's a screenshot: