Data aggregation

[patrickrobrecht]

Multiple rows with the same date, target and referrer can be aggregated with an additional column count.

• Database migration (add column count, migrate existing data)
• In the queries count(*) needs to be replaced with SUM(count).
• When adding a new row, check whether a row with that date, target and referrer exists already. If it exists, increase count, otherwise create it with count = 1.