* Scrollbars on overflow of horizontal nav

* Update _base.less

* Add fade out on right side of overflowing nav

* Update _base.less

- Update language choose dropdown to fit more languages

By adding a Japanese font in the less file, easier to see the display in
Japanese.

Collaborators have write access as default, and can be changed via repository
collaboration settings page to change between read, write and admin.

- Unified/Inline Diff-View Selectable

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

Most commit in Git are expected to follow standard of single header line,
followed by description paragraphs, separated by empty line from previous block.

Previously Gogs were treating everything as single header. Now we are trying to
render only first line as header, but following lines (description chunks) as a
verbatim.

Otherwise the fix will be overwritten by next _octicons.less update.

This is follow-up for 22b0dfbb35.

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