Request: ability to refresh/resync attached files

[hycday]

When adding an attachment in a list/tasks, it saves it in OpenTodoList as it is at that moment. If the file is later modified on the computer, then we can have a difference between the file in OpenTodoList and on the computer. Having a way to syncup the file to always pull the latest version and save it in OpenTodoList would be quite beneficial (could be done by checking if file is modified, or by enabling an option per attachment to pull do the check every x minutes, or any other way that leads to same results with minimal perf impact).