p-value calculations added

- p-value calculations added for nominal, ordinal and continuous dependent variable
- method for p-value adjustment added
- comments from previous PR #2264 addressed

[Reference](http://pic.dhe.ibm.com/infocenter/spssstat/v20r0m0/index.jsp?topic=%2Fcom.ibm.spss.statistics.help%2Falg_tree-chaid.htm)