add icons to QTableView header based on the data type

[mispp]

different icons for:

• numeric (double, int, decimal,...)
• date and datetime
• character and text
• other
  • maybe json and specific postgres datatypes

might be of use:

https://stackoverflow.com/questions/10820919/how-to-display-icons-in-qtableview-via-a-custom-qabstractitemmodel