'Leave Project' and 'Leave Group' should be buttons

We are in the process of organizing our settings, and replacing the dropdown with a Settings tab.

Leave Project and Leave Group are currently options in the dropdown. However, they aren't settings, and shouldn't be in the Settings tab. Let's find the right places for these buttons.

We currently place our Request access and Withdraw request access button here:

Project

Screen_Shot_2016-10-17_at_1.33.40_PM

(Sidenote: the button above needs padding. It shouldn't be sitting right next to the download button)

Group

Screen_Shot_2016-10-26_at_10.32.03_AM

I think placing the Leave project button here would make sense.

cc @tauriedavis @dzaporozhets @annabeldunstone

Related issues:

(meta) Give love to the settings screens (https://gitlab.com/gitlab-org/gitlab-ce/issues/22171)
Suggestion: Replace settings gear in projects/etc. with a tab (https://gitlab.com/gitlab-org/gitlab-ce/issues/23007)
Replace Group Settings with a tab (https://gitlab.com/gitlab-org/gitlab-ce/issues/23304)