Compatibility with data.table and tbl

[config-i1]

Need to check all the functions for the compatibility with "data.table" and "tbl" classes, so that they are used most efficiently and the functions still work.

This relates to: cramer, mcor, determ, assoc, tableplot, spread, alm, stepwise and lmCombine.

At the moment, the analytical functions just change the class to data.frame if they detect "data.table" or "tbl".

[config-i1]

alm() does not work with data.table() in some cases of data with factors. Not clear why. This needs to be fixed.

[config-i1]

It actually looks like a conflict of one of data.table functions.

[config-i1]

Fixed. But the fundamental issue is still there: a better support for data.table is needed.