feat: provide another styling theme (#779)

* feat: provide another styling theme
- the theme was copied from [vue-slimgrid](https://github.com/rob-white/vue-slimgrid) project and adjusted a bit, not perfect but provides a bit more modern styling theme

* chore: tweak styling theme a bit more for column picker

* chore: tweak styling theme a bit more

* chore: a bit more tweaks to new styling theme and another example

* chore: more styling theme tweaks

* chore: decrease new styling theme menus font size