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)

add ID to upload form and check if ID exist to avoid loading invalid javascript code for read-only views.

used get_cfg_var() to get the real limit from php.ini instead of .ht_access
dont know why we used PHP_INT_MAX here...