Backend: mosaic plot.data class needs to support allStats for rxc tables #215

weve decided the SAM will have a single contingency table viz which returns whichever stats make sense given its size. we already have an allStats method for 2x2 tables, but need one for rxc as well. i think itd be ok to only return chisq results for now if needed. the panelAllStats fxn also needs to get smarter, to detect the size of the table i suppose. finally, we need to be careful bc the S4 methods for the stats produce a slightly differently shaped stats table than the old chisq fxn did. we need to support both until the eda rxc mosaic api gets updated.