Refactor: Collect all data as references to records

[heikkilevanto]

Do not collect various hashes and arrays when reading the file. Instead, collect references to the record in various hashes, for example $restaurants{$restauranttype} = $rec That way, we can access not only the restaurant name, but the last time we visited it, and several other details. In time this will make small lists easier to manage.

[heikkilevanto]

Or maybe just store the index in @records for the first (or last) entry for each date, and take it from there.

[heikkilevanto]

Collecting first- and lastdateindex for each effdate. Using them in plotting the graph. This is the way to go.