data: refreshing with DB

* database stores modification time of files.
* FileManager updates internal state based on database info.
* reimplemented FileManager's check if a file is in project.
* implemented clearing data of updated or removed files before reparsing the updated and added files.

src/lib/utility/utility.h

@@ -4,6 +4,9 @@
 #include <deque>
 #include <chrono>
 #include <set>
+#include <time.h>
+
+#include "boost/date_time/posix_time/posix_time.hpp"
 
 #include "utility/math/Vector2.h"
 
@@ -15,6 +18,9 @@ namespace utility
 	float duration(const TimePoint& start);
 	float duration(std::function<void()> func);
 
+	std::string timeToString(const time_t time);
+	std::string timeToString(const boost::posix_time::ptime time);
+
 	template<typename T>
 	std::vector<T> concat(const std::vector<T>& a, const std::vector<T>& b);