doc: add better description for initial dev setup

If a developer hadn't use such a setup before, it is a little hard
to setup a development environment. This change adds more explicit
steps to setup everything.
refactor: grunt configuration

* split up configuration into modules
* clean coding style
fix sounds for pacman

pacman missed all the sounds :( shame on me.
add eslint to enforce consistent coding style

coding style should be consistant in a project. Using tools like eslint
will help enforcing the style all contributors agreed on.
fix all linting errors

code domina is happy, now
enable eslint task during build

never ever make the code domina unhappy, again
remove html5slider