Use a different Date data type

PLEASE backup your database before testing this commit, and report any
migration issue.

In postgresql, we use timestamp with timezone.
In sqlite3 we use REAL (the date is expressed as julianday)

This requires a migration of the muclogline_ table:
In postgresql it’s pretty simple, we convert all the integer into timestamps

With sqlite3, we actually rename the table, create the new one with the
correct type, then copy everything to the new table, with a conversion
function for the Date_ column, and then we delete the old table.

fix #3343

src/database/sqlite3_engine.hpp

@@ -23,12 +23,19 @@ class Sqlite3Engine: public DatabaseEngine
   ~Sqlite3Engine();
 
   static std::unique_ptr<DatabaseEngine> open(const std::string& string);
+  EngineType engine_type() const override
+  {
+    return EngineType::Sqlite3;
+  }
 
-  std::set<std::string> get_all_columns_from_table(const std::string& table_name) override final;
+  std::map<std::string, std::string> get_all_columns_from_table(const std::string& table_name) override final;
   std::tuple<bool, std::string> raw_exec(const std::string& query) override final;
   std::unique_ptr<Statement> prepare(const std::string& query) override;
   void extract_last_insert_rowid(Statement& statement) override;
-  std::string id_column_type() override;
+  std::string id_column_type() const override;
+  std::string datetime_column_type() const override;
+  void convert_date_format(DatabaseEngine&) override;
+  long double epoch_to_floating_value(long double d) const override;
 private:
   sqlite3* const db;
 };