Add ability to enter sheet properties

[gdoteof]

For my project I need the ability to color the tabs. This is done in the sheetProperties class.

Please see:

https://msdn.microsoft.com/en-us/library/documentformat.openxml.spreadsheet.sheetproperties(v=office.14).aspx

For example to set a sheet_names tab to blue:

workbook['Sheets'][sheet_name]['!sheetPr'] = [{tabColor: {theme: "3", tint: "-0.249977111117893"}}];