Mimic LibreOffice cell typeguessing

[gorn]

This is a feature request and needs some more investigation. LibreOffice does very good job in setting default styles for cells when the cell is the only one set in a column. It stores this info to column information. Rspreadsheet should respect this value (and do not add additionall style value to a cell) and make use of it (in guessing types of a cell).