Accessible $fetchfieldsList on GoogleSheetDataSource

[lintaba]

For extension (and for teams support) we need access to FETCHFIELDS_GET and FETCHFIELDS_LIST. Its now a calculated field, and their corresponding calculated values are in private variables.

Currently I had to copy GoogleSheetDataSource constructor calls to have the same properties, but its now just an ugly hack.

Solution 1:

private $fetchfieldsGet = '';
private $fetchfieldsList = ''; 

Could become protected

Solution 2:
a protected getter for fetchfieldsGet and fetchfieldsList.