* Fix gitgraph branch continues after merge

After fixing the initial problem in #11981 another
problem has come to light...

Fix #11981 (part 2)

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Update web_src/js/vendor/gitgraph.js

* Apply suggestions from code review

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

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

* Handle multiple merges in gitgraph.js

There is a bug in web_src/js/vendor/gitgraph.js whereby it fails to
handle multiple merges in a single commit correctly. This PR adds
changes to make this work.

Fix #11981

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Update web_src/js/vendor/gitgraph.js

- lowercase all js filenames except Vue components
- enable new lint rules, mostly focused on shorter code
- autofix new lint violations
- apply misc transformations indexOf -> includes and onevent-> addEventListener

Co-authored-by: Antoine GIRARD <sapk@users.noreply.github.com>

- move "vendor" files to js/vendor and less/vendor
- move swagger to js/standalone (meant for standalone pages)
- move gitgraph to features and streamline its loading
- add linting configs to webpack dependencies in make
- set ignored files for eslint/stylelint directly in their configs

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Antoine GIRARD <sapk@users.noreply.github.com>

This is the result of `make npm-update`. I also fixed a minor linting
issue which came up with the eslint 6.7 update.

* move semantic.dropdown.custom.js to webpack

Also disabled a annoying linter rule which insisted that imports can not
contain a file extension.

Fixes: https://github.com/go-gitea/gitea/issues/8971

* reorganize web_src files and rebuild

* restart ci

- moved gitgraph.js to web_src and made it importable and es6-compatible
- created new webpack chunk for gitgraph
- enabled CSS loader in webpack
- enabled async/await syntax via regenerator-runtime
- added script to ensure webpack chunks are loaded correctly
- disable terser's comment extraction to prevent .LICENCE files

gitgraph.js has many issues:

1. it is incompatible with ES6 because of strict-mode violations
1. it does not export anything
1. it's css has weird styles like for `body`
1. it is not available on npm

I fixed points 1-3 in our version so it's now loadable in webpack. We should eventually consider alternatives.