reintroduce download button on public shares

Backport of df32254 from master
remove file name from upper right button

Backport of 003049e from master
remove unneeded header-right details styles

Backport a280a69
fix position and look of public download button

Backport of 899c7c0 from master
disable download button if zip download is disabled

Backport of 6e75b37
Merge pull request #9511 from owncloud/stable6-download-button-public-folder

[stable6] Bring back the download button public folder