Being the good boyscouts, but mainly because of [the comment in the
review](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12378#note_33302115)
the words used for classes and variables are changed to not use builds
anymore.
* fix commit duration graph
* make graphs responsive
* fix wrong padding
* add a bit of explanation to colors
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>