Bug 31528: Replace scss-lint configuration with one for stylelint

Bug 31528: Replace scss-lint configuration with one for stylelint

This patch removes the SCSS linting configuration .scss-lint.yml which
was intended to be used with a now-obsolete tool, scss-lint.

It is replaced with .stylelintrc.json, for use with stylelint. I've
tried to keep the linting rules the same as before.

To test, run 'yarn install' to install the new dependencies.

You can test stylelint from the command line like so:

npx stylelint koha-tmpl/intranet-tmpl/prog/css/src/staff-global.scss

It should output a list of problems with the file:

koha-tmpl/intranet-tmpl/prog/css/src/staff-global.scss
   30:27   ✖  Expected "#e6f0f2" to be "#E6F0F2" color-hex-case
   81:31   ✖  Expected single space after "("    function-parentheses-space-inside
   ...etc.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>