Harden deinstallation of nginx default config.

git-svn-id: http://svn.code.sf.net/p/openmediavault/code/trunk@1107 3c3d7b80-5828-415e-9f61-280b98178fff
Select the 'System information' tree node per default. The 'About' is only used as fallback (e.g. when a user logs in).

git-svn-id: http://svn.code.sf.net/p/openmediavault/code/trunk@1109 3c3d7b80-5828-415e-9f61-280b98178fff
Add environment variables OMV_NGINX_SITE_WEBGUI_SECURITY_CSP_ENABLE and OMV_NGINX_SITE_WEBGUI_SECURITY_XFRAMEOPTIONS_ENABLE. Set to 'no|NO|0|false|FALSE' in '/etc/default/openmediavault' to disable these security options.

git-svn-id: http://svn.code.sf.net/p/openmediavault/code/trunk@1110 3c3d7b80-5828-415e-9f61-280b98178fff