Try to merge into develop branch ASAP, then continue minor fixes afterwards.

Closes #3182

* render code view server side

* remove debug print

* fix multiline selection bug

* change string concatenation to bytes.Buffer for efficiency

* Fix newlines added by previous for hljs

* fix selection highlighting

* make css changes in .less

* Lighter icon colors for repo files

* also color submodule icon

- add border-radius to filter list items
- use color as background of label for issue/pull view page

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

- 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.