Trashbin improvements

Some trash bin improvements:

- nicer unique names (file (restored).txt instead of file.txt.restored) ( #3131 )
- don't copy empty folders to the trash
- disable "deleted files" button if the trash bin is empty (#4114)
- expire trash if a new file was uploaded and the trash bin exceeds the new max size
- hide delete permanently button during restore ( https://github.com/owncloud/core/issues/2856)

UPD by vicdeo added one more link to related issue

cc @jancborchardt