less: use upstream's dataTables.bootstrap style instead of jquery.dataTables.css

See https://datatables.net/examples/styling/bootstrap.html .

- use official dataTables.bootstrap.css and dataTables.bootstrap.js
- add datatable less style block to use kallithea font icons
- move dataTables related style to this new block to have them in one place
- remove style that is obsolete, overrides or gets overriden by dataTables.bootstrap.css