Refresh single node PIP/SNIP/CDI #311

In the network tree view I would like to right click a single node, see a popup menu, and select Reload.
This action should do the following:

• send a new snip request
• send a new pip request
• forget the CDI for the node

Why:

• there is no way today to forget the CDI (short of restarting JMRI)
• if the SNIP/PIP requests timeout, there is no way to trigger them again without rebooting the node; however, rebooting the node can only be done inside the CDI dialog which you can not open if the PIP request did timeout.
• doing refresh all can cause the SNIP/PIP to timeout if the network is really big (I think there is a bug lurking here somewhere but I was not able to pin it down yet).

While at it:

• in the popup menu for a single node, we could also add a "restart device" item. This would send a memory config datagram to reboot.
• in the right-click popup menu of the toplevel item, we could add an "expand all" item that makes every node opened up (once level only, just so that the version numbers are visible). Similarly a "Collapse all".