Store statistical data without time limit

[zepich]

To see how many submissions were handled by mosparo and to speed up the database queries to get the statistical information, the idea is to add a separated database table in which the statistical data is stored independently from the submissions.

These statistical data will kept without a time limit (forever).

Required features

• Store the historical data in a separate table
• Adjust the dashboard query to use this table only
• Adjust the Statistic API to use this table only
• Add a date range option to select the visible range of the statistical data on the dashboard

Optional additional features

• Add a setting to clean up the historical data after a specified number of days (for example, 365 days)
• Add a CLI command to clean up the historical data
• Add a UI function to clean up the historical data

Origin

Issue #121