Add some kind of identifier for incomplete files

[Titokhan]

There's an option in µTorrent to append .!ut to incomplete files, which is helpful if other apps/modules are using the files simultaneously. They can easily identify and blacklist those.

Right now, pSync creates the file object inside 'Working' folder with the original name and fills it up, depending on the availability. Other modules, such as the map visualizator or KMZ parser often find invalid files as the transfer may not be completed. To overcome this issue, pre-validation of KMZ has been added inside the workflow of those modules, but it would be better pSync has the capability.

It can also be possible to create a temporary folder for storing the incomplete files and transfer them inside the 'Working' one after it's being fully transferred.