ClearRows() should initialize with new NewStringData()

[JoeyFreeland-DojoFive]

Describe the bug
The ClearRows() method of a table sets the data to nil, but in the New() function to create a new table model, it is set to NewStringData(). Therefore if you want to clear a table of all its rows, you will not be able to add rows later. Rows will only be appended if the type of the internal data is StringData, which is not true after calling ClearRows().

Source Code
table.go