Translation for exporter.py

This is dangerous. Don't translate global variables. Instead, you will have to modify this so that:
```
def get_data_keys():
	return frappe._dict({
		"data_separator": _('Start entering data below this line'),
		"main_table": _("Table:"),
		"parent_table": _("Parent Table:"),
		"columns": _("Column Name:"),
		"doctype": _("DocType:")
	})
```
and replace use of data_keys with get_data_keys()