make files_versions use OC_User::getHome, fixes 'PHP Warning:  Missing argument 1 for OC_FilesystemView::getAbsolutePath' with custom user home dirs

only check if #dropdown hasClass drop-versions if a drop down is open. Otherwise it will never open the history drop-down

fix missing dir creation for file versions (OC_Filesystemview::mkdir doesn't work here because it doesn't create directories recursively)

automatically remove and prevent installation of apps with a require version less than the current one. We check now the first ad second part of the version number.
Also increase the require tags of the core apps to 4.9 Please note that 4.9 is the internal versionnumber of the upcoming 4.5 release.
You have to pu a <require>4.9</require> into the info.xml of your app to make it as compatible with 4.5

This didn't work with chunked uploading