Replace anchors with no real href with buttons

Closes #3101 & #916

**Important**: As soon as this is merged, I need to tag & release a new version of Ghost-UI, as these changes  may make things look rather broken without the amended styles.

Related style changes are https://github.com/TryGhost/Ghost-UI/commit/6ec8e26d8f5c3d7975d8900b8a810d3fde922418
Just delete tag name here; gh-popover-bttton is a button by default