ui: file not up to date display

* the codeview now displays a hatched background for a filename when the file's content has changed or the file does not exist anymore.
* added TimePoint class to encapsulate boost.

src/lib/data/Storage.cpp

@@ -5,6 +5,7 @@
 
 #include "utility/file/FileSystem.h"
 #include "utility/logging/logging.h"
+#include "utility/TimePoint.h"
 #include "utility/utility.h"
 #include "utility/utilityString.h"
 
@@ -1219,6 +1220,11 @@ std::shared_ptr<TextAccess> Storage::getFileContent(const FilePath& filePath) co
 	return m_sqliteStorage.getFileContentByPath(filePath.str());
 }
 
+TimePoint Storage::getFileModificationTime(const FilePath& filePath) const
+{
+	return TimePoint(m_sqliteStorage.getFileByPath(filePath.str()).modificationTime);
+}
+
 Id Storage::addNodeHierarchy(Node::NodeType nodeType, NameHierarchy nameHierarchy, bool defined, bool distinct)
 {
 	std::vector<Id> nameIds = addNameHierarchyElements(nameHierarchy);