Added ability to specify a custom function for checking menu access (accessFn)

Change-Id: Iafecfa12963562692b0256df1389f326c58c0607

Change-Id: Iacad7a1066c5984fedd80288425256548e2b54a0
1. /vcenter/login does authentication via vCenter auth plugin

2. Read the current orchestration mode from
webServerInfo.loggedInOrchestrationMode

3. Set the default landing page to Monitor > Networks in case of vCenter

4. Redirect to '/vcenter/login' on '/login' if vCenter is only orchestration
model

5. Display only vcenter projects

Change-Id: Ib74afe8b6347115ab2a87366f85d24ef9c83e23f

Change-Id: If651ca1d43b6acb094b50c0d48aebe7841eded5c