* Server-side syntax hilighting for all code

This PR does a few things:

* Remove all traces of highlight.js
* Use chroma library to provide fast syntax hilighting directly on the server
* Provide syntax hilighting for diffs
* Re-style both unified and split diffs views
* Add custom syntax hilighting styling for both regular and arc-green

Fixes #7729
Fixes #10157
Fixes #11825
Fixes #7728
Fixes #3872
Fixes #3682

And perhaps gets closer to #9553

* fix line marker

* fix repo search

* Fix single line select

* properly load settings

* npm uninstall highlight.js

* review suggestion

* code review

* forgot to call function

* fix test

* Apply suggestions from code review

suggestions from @silverwind thanks

Co-authored-by: silverwind <me@silverwind.io>

* code review

* copy/paste error

* Use const for highlight size limit

* Update web_src/less/_repository.less

Co-authored-by: Lauris BH <lauris@nix.lv>

* update size limit to 1MB and other styling tweaks

* fix highlighting for certain diff sections

* fix test

* add worker back as suggested

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lauris BH <lauris@nix.lv>

* Add octicon SVG sprite

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Static prefix

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* SVG for all repo icons

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* make vendor

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Swap out octicons

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Move octicons to top of less imports

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Fix JS

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Definitely not a search/replace

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Missed regex

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Move to more generic calls and webpack

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* make svg -> make webpack

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Remove svg-sprite

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Update tests

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Missed a test

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Remove svg from makefile

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Suggestions

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Attempt to fix test

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Update tests

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Revert timetracking test

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Swap .octicon for .svg in less

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Add aria-hidden

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Replace mega-octicon

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Fix webpack globbing on Windows

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Revert

Co-Authored-By: silverwind <me@silverwind.io>

* Fix octions from upstream

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Fix Vue and missed JS function

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Add JS helper and PWA

Signed-off-by: jolheiser <john.olheiser@gmail.com>

* Preload SVG

Signed-off-by: jolheiser <john.olheiser@gmail.com>

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <matti@mdranta.net>

* update #8659 fold/unfold code diffs

* add fold button style

* update #8659 implement expand up/down codes (blob excerpt)

* fix golint errors

* fix expand direction

* remove debug message

* update css style for blob exceprt

* fix typo in comment

* update style sheet with less

* update expect diff (add SectionInfo)

* update #8942 accept suggested change (fix typo)

* close reader and check file type before get tail section

* adjust button position and check file type before insert fold button

* move index js to web_src

* merge index.js with master

* generate index.js

* update js coding style