- added new 'make webpack' target
- deprecated 'make js' and 'make css'
- extend webpack config to load the less files
- updated docs

I had to rename the source file of `arc-green.less` to avoid generating
a useless JS entrypoint via webpack-fix-style-only-entries which would
not work with different source/destination filenames. I hear that there
should be cleaner solutions possible once we upgrade to Webpack 5.

Co-authored-by: zeripath <art27@cantab.net>

- Added Node.js as build dependency and removes build files from git.
- Added version checks for both Go and Node.js.
- Overhauled the js/css make target to only run when needed.
- Merged the `generate` make target into `build` as per suggestion.

Fixes: https://github.com/go-gitea/gitea/issues/6782
Fixes: https://github.com/go-gitea/gitea/issues/9216

* Add USE_SERVICE_WORKER setting

This will be very useful setting for anyone doing frontend work.

Fixes: https://github.com/go-gitea/gitea/issues/9044

* prevent potential syntax error on old browsers

* Add 'make revive' to instructions for checking code

This is performed on drone, hacking instructions should contain the same to avoid unnecessary PR builds.

* lint is deprecated. Denote revive +vet as code analysis in continuous text.

Fix spelling of misspell in command to validate swagger.

* use vendors when go generate

* update docs about golang minimal requirement from 1.9 to 1.11

* fix build

* add 'npm' and 'npm-update' make targets and lockfile

- `make npm` installs and updates node_modules, triggered automatically
   on `make css` and `make js` as it completes reasonably fast and
   ensures consistent modules.
- `make npm-update` updates all dependencies to their latest version,
   regenerates `node_modules` from scratch and updates
   `package-lock.json`. It uses npm modules `updates` written by yours
   truly to find the latest version of each dependency.

* add suggested make dependencies

* remove package-lock.json during npm-update

* regenerate package-lock.json

* add make targets for js,css, add javascript linter

- add `make js`, deprecating `make javascripts`
- add `make css`, deprecating `make generate-stylesheets` and
  `make stylesheets-check`
- changed the unclean css check to only run on CI
- add JS linting via eslint with basic configuration and fixed
  discovered issues
- changed autoprefixer to use official `postcss-cli` avoiding the need
  to loop in the makefile
- moved browserslist to package.json so other future tools can use it
  too.
- update documentation for new make targets and added JS section

* fix indentation

* move functions used in html to 'exported' list

* Run lessc binary without having to install anything to node_modules

* use relative paths to node bin scripts, removing npx

* Revert "use relative paths to node bin scripts, removing npx"

This reverts commit 119b725525.

* fix lessc and postcss plugins

* check for node_modules and use actual bin names

* Added Go Path and node_modules to PATH
* Uses npx now for generate-stylesheets
* Uses `go env GOPATH` to calculate adding GOPATH/bin to PATH
* Added note about installing Node 8.0+ to generate stylesheets
* Added preferred Node version to CONTRIBUTING.md

* Update and expand building information

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

* remove extraneous extra line

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

* Fix spelling mistake

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

* Note about documentation for the website

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

* More changes

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

* Clarified the automatic build dependency

* Update the from-source to match the hacking information

* Extend quotes

* Update required go and discord link

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

* Update hacking-on-gitea.en-us.md

Add in information about postcss

* Clean up spelling, grammar, perspective, whitespace, language, markup, etc.

* import docs into main repository

Signed-off-by: Matti Ranta <matti@mdranta.net>