[manage view] cleanup manage view and user menu
* drop code that shouldn't be there (e.g. folders handling)
* add a section displaying site management actions, some of them
were initially in the user's drop down menu, which now only have
a 'manage' link with regards to management actions
* stop displaying 'system' and 'schema' entities by default, only
'application' entities
* put 'gc', 'registry' and 'info' views as tabs of a generic
'server information' view