Added system selection to the mining spreadsheet.
Right now it only allows to select a system. In the future the user will
have to select a region then it will load the systems in that region, giving
the option to not specify the system and query the entire region instead.
Added region selection to the mining spreadsheet.

Also, system selection now depends on user selecting a region first, which
then loads the select field with the systems from that region.

The system field may be left blank for a whole region query.