Potential conflict of interest
Disclosure forms provided by the authors are available with the full text of this article at http://dx.doi.org/10.1080/10428194.2016.1251593.
Funding
This work was supported by Scientific Grant Agency of Ministry of Education, Science, Research and Sport of Slovak Republic and Slovak Academy of Sciences [VEGA 1/0905/12], Internal Scientific Grant System of P.J. Safarik University [VVGS-2014-198] and Grant System of Doctorands of P.J. Safarik University [22/GSD/2016].