Codechange: introduce a framework for all our timers

IntervalTimer and TimeoutTimer use RAII, and can be used to replace
all the time-based timeouts, lag-detection, "execute every N" we
have.
As it uses RAII, you can safely use it as static variable, class
member, temporary variable, etc. As soon as it goes out-of-scope,
it will be safely removed.
This allows for much easier to read code when it comes to intervals.

src/timer/timer_window.cpp

@@ -0,0 +1,60 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @file timer_window.cpp
+ * This file implements the timer logic for the Window system.
+ */
+
+#include "stdafx.h"
+#include "timer.h"
+#include "timer_window.h"
+
+#include "safeguards.h"
+
+template<>
+void IntervalTimer<TimerWindow>::Elapsed(TimerWindow::TElapsed delta)
+{
+	if (this->period == std::chrono::milliseconds::zero()) return;
+
+	this->storage.elapsed += delta;
+
+	uint count = 0;
+	while (this->storage.elapsed >= this->period) {
+		this->storage.elapsed -= this->period;
+		count++;
+	}
+
+	if (count > 0) {
+		this->callback(count);
+	}
+}
+
+template<>
+void TimeoutTimer<TimerWindow>::Elapsed(TimerWindow::TElapsed delta)
+{
+	if (this->fired) return;
+	if (this->period == std::chrono::milliseconds::zero()) return;
+
+	this->storage.elapsed += delta;
+
+	if (this->storage.elapsed >= this->period) {
+		this->callback();
+		this->fired = true;
+	}
+}
+
+template<>
+void TimerManager<TimerWindow>::Elapsed(TimerWindow::TElapsed delta)
+{
+	/* Make a temporary copy of the timers, as a timer's callback might add/remove other timers. */
+	auto timers = TimerManager<TimerWindow>::GetTimers();
+
+	for (auto timer : timers) {
+		timer->Elapsed(delta);
+	}
+}