Implement Data Collection

Design idea: "Prepare iteration"

DataCollection collects all stations of interest with all inputs (including the grid data, neighbors, ...). DataCollection itself doesn't handle the inputs and neighbors but just collects ready to use data classes (see #141 (closed)).

Jobs:

• collect all stations (data is collected as list of elements)
• has method iter
• calls iterator (StandardIterator from #143 (closed))