UI: standardising text for "VM"

* replaces “Working Environments” -> “Virtual Machines”
* ( addresses #425 )
UI: adds option to exclude experiment from a page

* ( addresses #477)
UI: removes ATLAS VM section + page

* (closes #477)
LHCb: introduce VM page

* ( closes #499)
LHCb: introduce getting started page

* (closes #500)