- Unified/Inline Diff-View Selectable

- User profile un/follow
- List user's followers/following

This does not change any content and generated gogs.css is still the same.

With grey SHA1 labels, we should consider having also more subtle strips on
commits list. As current strips blend too much with grey SHA1 labels and top
bar, making hard to distinguish headers from content.

This removes remains from old design, that was not cleaned by previous #2068 PR.

This uses a CSS trick making first th to be relative block with width equal to
first two columns, effectively working around inability to use colspan="2" on
first row that was breaking "fixed-layout" for tables.

Also use grey header for last-commit SHA1 tag.

Just use secondary menu instead custom ".head.meta", which simplifies code.

Also do not display repo URL action when we are in subdirectory or viewing a
file.

This is more inline with way GitHub looks like and feels much more natural and
in style with rest of the interface.

Instead using own ellipsis, uses Semantic UI fixed single line table which
effectively applies ellipsis to all overflowing table cells.

NOTE: File list cannot use colspan="2" for 1st "Last commit" elements,
otherwise layout breaks with fixed table.

This is because SHA1 label is used in many other places, not only inside
.repository container.

- copy link button: #1396, #1168, #1668,
- synxtax highlight: #1712, #1549, #1315, #670
- z-index: #1942

Signed-off-by: Unknwon <u@gogs.io>