Create time tracking landing page

Goal

Create landing page for upcoming EE product, time tracking. The page URL will be about.gitlab.com/features/time-tracking

ToDo

• Copy page structure from GitLab Geo
• Remove the already an enterprise customer CTA since we are giving time tracking away for free while it is in beta
• Insert new copy: https://docs.google.com/a/gitlab.com/document/d/15usW41-cCkR6gdm_6pOIGM-b4YFhhE8XGjdQLIABJ90/edit?usp=sharing
• Insert new icons for the how it works and benefits sections
• Add Time Tracking to the EE product pages nav