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/utils/datetime.hpp

@@ -0,0 +1,68 @@
+#pragma once
+
+#include <chrono>
+#include <string>
+
+#include <logger/logger.hpp>
+
+class DateTime
+{
+public:
+  enum class Engine {
+    Postgresql,
+    Sqlite3,
+  } engine{Engine::Sqlite3};
+
+  using time_point = std::chrono::system_clock::time_point;
+
+  DateTime():
+      s{},
+      t{}
+  { }
+
+  DateTime(std::time_t t):
+      t(std::chrono::seconds(t))
+  {}
+
+  DateTime(std::string s):
+      s(std::move(s))
+  {}
+
+  DateTime& operator=(const std::string& s)
+  {
+    this->s = s;
+    return *this;
+  }
+
+  DateTime& operator=(const time_point t)
+  {
+    this->t = t;
+    return *this;
+  }
+
+  const std::string& to_string() const
+  {
+    return this->s;
+  }
+
+  time_point::duration epoch() const
+  {
+    return this->t.time_since_epoch();
+  }
+
+  long double julianday() const
+  {
+    log_debug("ici?");
+    auto res = ((static_cast<long double>(this->epoch().count()) / std::chrono::system_clock::period::den) / 86400) + 2440587.5;
+    return res;
+  }
+
+private:
+  std::string s;
+  time_point t;
+};
+
+inline long double to_julianday(std::time_t t)
+{
+  return static_cast<long double>(t) / 86400.0 + 2440587.5;
+}