[BUGFIX] Paste button missing in empty folders

Inside an empty folder is no obvious way to paste the content of the
clipboard.

Add a paste icon to the docheader to paste into the current folder.

Resolves: #48202
Releases: 6.2, 6.1, 6.0
Change-Id: I2192bd853a1c1fada332319812acee8fe821b78a
Reviewed-on: https://review.typo3.org/20936
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters