Add a trash like the one on the desktop OS

[Leo Arias]

Now users can recover deleted files, as fixed by Diogo on bug #377905.
That's a nice first step to reduce the amount of support requests we receive every day, but the feature is still not what people is used to have.

We are used to get a trash folder handled by the operating system, where we can select which files or folders we want to recover.

I would like all the files and folders deleted from Ubuntu One to go to this trash folder, that's not synchronized to the devices. The users should be able to go to this folder and select the things they want to recover, and those should be moved to their original place.