Set timestamps for Siafile
This MR adds some code that updates the timestamps of the SiaFile correctly. There are 4 timestamps in total which need to be set:
ModTime
- whenever the content of the file changes
ChangeTime
- whenever the metadata of the file changes
CreateTime
- when the file is created / uploaded to the network
AccessTime
- whenever the file is accessed
Edited by Christopher Schinnerl