Add statistics support for Sqlite by tweeking one query and rewrite an other. The rewrite implied a complete refactor of the MySql query as well. Now the code is more flexible and make less queries to the database. See #527
Temporarily disable 30-day statistics for SQLite https://github.com/marienfressinaud/FreshRSS/issues/100 https://github.com/marienfressinaud/FreshRSS/issues/90