Move issue title to the top of the page [Awaiting developper feedback]

Created by: cirosantilli

Every time I look at a GitLab issue I feel my eyes wondering for 2 seconds to find the title.

Titles should be one of the first things we see on pages.

After: remove "Issue" since already on the tab, put the title there, de-emphasize the id with a gray color:

Before:

It gets even worse if there are headers in the description, since even an h2 is larger than the title:

This is also closer to how GitHub looks.

If you like this, it should also be done for merge requests and milestones simultaneously.